U.S. patent number 7,824,937 [Application Number 10/548,560] was granted by the patent office on 2010-11-02 for solid element device and method for manufacturing the same.
This patent grant is currently assigned to Sumita Optical Glass Inc., Toyoda Gosei Co., Ltd.. Invention is credited to Kazuya Aida, Kunihiro Hadame, Mitsuhiro Inoue, Hideaki Kato, Masaaki Ohtsuka, Koichi Ota, Naruhito Sawanobori, Yoshinobu Suehiro, Ryoichi Tohmon, Satoshi Wada, Hiroki Watanabe, Yoshinori Yamamoto.
United States Patent |
7,824,937 |
Suehiro , et al. |
November 2, 2010 |
Solid element device and method for manufacturing the same
Abstract
A method for manufacturing a solid element device, which
comprises providing a glass-containing Al.sub.2O.sub.3 substrate
(3) having a GaN based LED element (2) placed thereon, setting a
P.sub.2O.sub.5--ZnO based low melting point glass in parallel with
the substrate, and carrying out a press working at a temperature of
415.degree. C. or higher under a pressure of 60 kgf in a nitrogen
atmosphere. Under these conditions, the low melting point glass has
a viscosity of 10.sup.9 poise, and is adhered via an oxide formed
on the surface of the glass-containing Al.sub.2O.sub.3 substrate
(3). A solid element device manufactured by the above method can be
manufactured through a glass sealing working at a low temperature
and also has a highly reliable sealing structure.
Inventors: |
Suehiro; Yoshinobu (Aichi-ken,
JP), Inoue; Mitsuhiro (Aichi-ken, JP),
Kato; Hideaki (Aichi-ken, JP), Hadame; Kunihiro
(Aichi-ken, JP), Tohmon; Ryoichi (Aichi-ken,
JP), Wada; Satoshi (Aichi-ken, JP), Ota;
Koichi (Aichi-ken, JP), Aida; Kazuya
(Saitama-ken, JP), Watanabe; Hiroki (Saitama-ken,
JP), Yamamoto; Yoshinori (Saitama-ken, JP),
Ohtsuka; Masaaki (Saitama-ken, JP), Sawanobori;
Naruhito (Saitama-ken, JP) |
Assignee: |
Toyoda Gosei Co., Ltd.
(Nishikasugai-gun, Aichi-ken, JP)
Sumita Optical Glass Inc. (Saitama-shi, Saitama-ken,
JP)
|
Family
ID: |
32996669 |
Appl.
No.: |
10/548,560 |
Filed: |
March 10, 2004 |
PCT
Filed: |
March 10, 2004 |
PCT No.: |
PCT/JP2004/003089 |
371(c)(1),(2),(4) Date: |
November 25, 2005 |
PCT
Pub. No.: |
WO2004/082036 |
PCT
Pub. Date: |
September 23, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060261364 A1 |
Nov 23, 2006 |
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Foreign Application Priority Data
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Mar 10, 2003 [JP] |
|
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2003-063015 |
Jun 5, 2003 [JP] |
|
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2003-160855 |
Jun 5, 2003 [JP] |
|
|
2003-160867 |
Jul 7, 2003 [JP] |
|
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2003-193182 |
Sep 30, 2003 [JP] |
|
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2003-342705 |
Sep 30, 2003 [JP] |
|
|
2003-342706 |
Jan 19, 2004 [JP] |
|
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2004-010385 |
|
Current U.S.
Class: |
438/26;
257/E21.504 |
Current CPC
Class: |
C03C
27/06 (20130101); C03C 8/24 (20130101); H01L
24/17 (20130101); H01L 33/56 (20130101); H01L
2924/12041 (20130101); H01L 2224/48227 (20130101); H01L
24/73 (20130101); H01L 2224/32225 (20130101); C03B
23/20 (20130101); H01L 2224/45144 (20130101); H01L
24/45 (20130101); H01L 2224/48465 (20130101); H01L
2224/73265 (20130101); H01L 2224/48091 (20130101); H01L
2924/12036 (20130101); H01L 2924/181 (20130101); H01L
2224/97 (20130101); H01L 2224/92125 (20130101); H01L
2924/12035 (20130101); H01L 2933/005 (20130101); H01L
2224/14 (20130101); H01L 2224/73204 (20130101); H01L
2924/12042 (20130101); H01L 2224/48247 (20130101); H01L
2924/3025 (20130101); H01L 2224/16225 (20130101); H01L
2224/48237 (20130101); H01L 2924/01322 (20130101); H01L
2224/48257 (20130101); H01L 2924/01057 (20130101); H01L
2924/15787 (20130101); H01L 2224/48091 (20130101); H01L
2924/00014 (20130101); H01L 2224/73265 (20130101); H01L
2224/32225 (20130101); H01L 2224/48227 (20130101); H01L
2924/00012 (20130101); H01L 2224/48465 (20130101); H01L
2224/48091 (20130101); H01L 2924/00012 (20130101); H01L
2224/48465 (20130101); H01L 2224/48227 (20130101); H01L
2924/00012 (20130101); H01L 2224/73204 (20130101); H01L
2224/16225 (20130101); H01L 2224/32225 (20130101); H01L
2924/00 (20130101); H01L 2924/01322 (20130101); H01L
2924/00 (20130101); H01L 2224/48465 (20130101); H01L
2224/48227 (20130101); H01L 2924/00 (20130101); H01L
2224/48465 (20130101); H01L 2224/48091 (20130101); H01L
2924/00 (20130101); H01L 2224/48465 (20130101); H01L
2224/48247 (20130101); H01L 2924/00 (20130101); H01L
2224/45144 (20130101); H01L 2924/00014 (20130101); H01L
2924/3025 (20130101); H01L 2924/00 (20130101); H01L
2924/12041 (20130101); H01L 2924/00 (20130101); H01L
2224/92125 (20130101); H01L 2224/73204 (20130101); H01L
2224/16225 (20130101); H01L 2224/32225 (20130101); H01L
2924/00 (20130101); H01L 2924/15787 (20130101); H01L
2924/00 (20130101); H01L 2924/12035 (20130101); H01L
2924/00 (20130101); H01L 2924/12036 (20130101); H01L
2924/00 (20130101); H01L 2924/12042 (20130101); H01L
2924/00 (20130101); H01L 2924/181 (20130101); H01L
2924/00012 (20130101); H01L 2224/73265 (20130101); H01L
2224/32225 (20130101); H01L 2224/48237 (20130101); H01L
2924/00 (20130101) |
Current International
Class: |
H01L
21/56 (20060101) |
Field of
Search: |
;257/100,E21.504
;438/26 |
References Cited
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cited by examiner .
Japanese Office Action dated Nov. 6, 2007 with partial English
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|
Primary Examiner: Vu; David
Assistant Examiner: Taylor; Earl N
Attorney, Agent or Firm: McGinn IP Law Group, PLLC
Claims
What is claimed is:
1. A method of making a solid element device, said method
comprising: mounting a solid element on an electric power receiving
and supplying part; and pressing, by molds of a press, an inorganic
sealing material directly onto said solid element at a temperature
above a deformation point of said inorganic sealing material to
seal said solid element, wherein said solid element comprises a
light emitting diode (LED).
2. The method of making a solid element device according to claim
1, wherein said mounting is conducted by flip mounting.
3. The method of making a solid element device according to claim
1, wherein said mounting comprises conducting wire bonding and
covering said solid element and said wire bonding part by a heat
resistant member that prevents said solid element and said wire
bonding part from deformation.
4. The method of making a solid element device according to claim
1, wherein said sealing is conducted such that said inorganic
sealing material is processed in a viscosity state of more than
10.sup.6 poise.
5. The method of making a solid element device according to claim
4, wherein said sealing is conducted such that said inorganic
sealing material is processed under high viscosity conditions in a
range of 10.sup.8 poise to 10.sup.9 poise.
6. The method of making a solid element device according to claim
1, wherein said electric power receiving and supplying part
comprises an inorganic material substrate on a side of which said
solid element is mounted and to a backside of which an electrode is
formed led out, a plurality of solid elements being mounted on said
inorganic material substrate and being sealed with said inorganic
sealing material.
7. The method of making a solid element device according to claim
6, wherein said inorganic sealing material comprises a preformed
glass.
8. The method of making a solid element device according to claim
1, wherein the sealing is conducted in an oxygen free
atmosphere.
9. The method of making a solid element device according to claim
1, wherein the sealing is conducted by hot pressing.
10. The method of making a solid element device according to claim
1, wherein the inorganic sealing material comprises a glass
sheet.
11. A method of making a solid element device, said method
comprising: mounting a solid element on an electric power receiving
and supplying part; pressing an inorganic sealing material onto
said solid element at a temperature above a deformation point of
said inorganic sealing material to seal said solid element; and
disposing a first sheet of the inorganic sealing material on the
solid element and a second sheet of the inorganic sealing material
under the solid element prior to said pressing, wherein said
pressing comprises: placing an upper mold of a press to cover the
first sheet; placing a lower mold of the press to cover the second
sheet; and moving the upper mold and the lower mold of the press in
a predetermined direction to apply pressure to the first sheet and
the second sheet by said upper mold and said lower mold,
respectively, wherein said solid element comprises a light emitting
diode (LED).
12. The method of making a solid element device according to claim
1, wherein said pressing the inorganic sealing material onto said
solid element comprises pressing an upper surface and a lower
surface of the solid element by said molds of the press.
13. The method of making a solid element device according to claim
1, wherein said inorganic sealing material is in direct contact
with said solid element.
14. The method of making a solid element device according to claim
1, further comprising: disposing a first sheet of the inorganic
sealing material on the solid element and a second sheet of the
inorganic sealing material under the solid element prior to said
pressing.
15. The method of making a solid element device according to claim
14, wherein said molds of the press comprise an upper mold and a
lower mold, said pressing comprising: placing the upper mold of the
press to cover the first sheet; placing the lower mold of the press
to cover the second sheet.
16. The method of making a solid element device according to claim
15, wherein said pressing further comprises: moving the upper mold
and the lower mold of the press in a predetermined direction to
apply pressure to the first sheet and the second sheet by said
upper mold and said lower mold, respectively.
17. A method of making a solid element device, said method
comprising: flip-chip mounting a solid element on a ceramic
substrate on a surface of which a circuit pattern is formed;
pressing an inorganic sealing material on said solid element at a
temperature above a deformation point of said inorganic sealing
material to seal said solid element; and disposing a sheet of said
inorganic sealing material on the solid element prior to said
pressing, wherein said pressing comprises: placing an upper mold of
a press to cover said sheet; placing a lower mold of the press to
cover the ceramic substrate; and moving the upper mold and the
lower mold of the press in a predetermined direction to apply
pressure to the sheet and the ceramic substrate by said upper mold
and said lower mold, respectively.
18. The method of making the solid element device according to
claim 1, wherein said electric power receiving and supplying part
comprises an inorganic substrate formed in a plate shape.
19. The method of making the solid element device according to
claim 1, wherein said inorganic sealing material is selected from a
group consisting of SiO.sub.2--Nb.sub.2O.sub.5-based,
B.sub.2O.sub.3--F-based, P.sub.2O.sub.5--F-based,
P.sub.2O.sub.5--ZnO-based,
SiO.sub.2--B.sub.2O.sub.3--La.sub.2O.sub.3-based, and
SiO.sub.2--B.sub.2O.sub.3-based glasses.
20. The method of making the solid element device according to
claim 19, wherein said inorganic sealing material comprises
SiO.sub.2--Nb.sub.2O.sub.5-based or SiO.sub.2--B.sub.2O.sub.3-based
glasses.
21. The method of making the solid element device according to
claim 1, wherein said inorganic sealing material has a side face
formed by dicer cutting.
22. The method of making the solid element device according to
claim 21, wherein said solid element device has a rectangular shape
having said side face of said inorganic sealing material.
23. The method of making the solid element device according to
claim 1, wherein said electric power receiving and supplying part
has a heat dissipation pattern formed on a backside surface of said
electric power receiving and supplying part.
24. The method of making the solid element device according to
claim 23, wherein a plurality of light emitting diode elements are
mounted on said electric power receiving and supplying part.
Description
This application is based on Japanese Patent Application Nos.
2003-063015, 2003-160855, 2003-160867, 2003-193182, 2003-342705,
2003-342706, and 2004-010385, the entire disclosures of which are
incorporated herein by reference.
TECHNICAL FIELD
The invention relates to a solid element device (or solid-state
device) comprising an optical element sealed with a glass material,
and particularly to a solid element device using a low melting
glass material as a glass material.
BACKGROUND ART
Solid element devices comprising a solid element, such as a light
emitting diode, sealed with a light transparent resin material such
as an epoxy resin have hitherto been known. In such solid element
devices, it is known that, upon exposure to high intensity light,
the light transparent resin causes deterioration such as yellowing.
In particular, when a group III nitride-based compound
semiconductor light emitting element which emits short-wavelength
light is used, the light transparent resin near the element is
yellowed by high energy light generated from the element and the
heat generated from the element per se and, consequently, the light
takeout efficiency is often lowered to an extent that is not
negligible.
In order to prevent the deterioration of the sealing member, a
luminescent device using a low melting glass as a sealing member
has been proposed in Japanese Patent Laid-Open Nos. 1996-102553 and
1999-177129.
In the luminescent device described in Japanese Patent Laid-Open
No. 1996-102553, an LED element, a wire bonding part, and the
periphery of the upper end of a lead part are covered with a
sealing body 7 made of a transparent low melting glass. The low
melting glass used is that, for example, selenium, thallium,
arsenic, or sulfur has been added to bring the melting point to
about 130 to 350.degree. C. In this case, preferably, the low
melting glass has a melting point of 200.degree. C. or below (more
preferably 150.degree. C. or below).
According to the luminescent device described in Japanese Patent
Laid-Open No. 1996-102553, a problem of a change in color of the
sealing body to yellow with the elapse of time due to poor or weak
resistance to ultraviolet light possessed by the epoxy resin and
the like can be avoided.
On the other hand, the luminescent device described in Japanese
Patent Laid-Open No. 1999-177129 uses, as a sealing body covering
the LED light emitting element, a low melting glass having a
refractive index of about 2 which is close to the refractive index
of a GaN-based LED light emitting element, about 2.3.
According to the luminescent device described in Japanese Patent
Laid-Open No. 1999-177129, sealing of the LED light emitting
element with the low melting glass having a refractive index close
to the GaN-based LED light emitting element can reduce the quantity
of light, which is totally reflected from the surface of the LED
light emitting element and is returned to the inside, and can
increase the quantity of light, which is emitted from the LED light
emitting element and enters the low melting glass. As a result, the
emission efficiency of the chip-type LED and the like according to
the invention of the application is higher than the conventional
device in which the LED light emitting element has been sealed with
the epoxy resin.
According to the solid element devices using the conventional low
melting glass as the sealing member, although the glass is low
melting glass, high temperature fabrication should be carried out,
and, due to the hard material, in fact, disadvantageously, any
sample device cannot be provided by the continuation of the resin
sealing.
Accordingly, an object of the invention is to extract and solve
problems involved in the realization of inorganic material sealing
and to provide a solid element device, which can actually offer
expected effects by glass sealing, and a method for manufacturing
the same.
DISCLOSURE OF THE INVENTION
In order to attain the above object, the invention provides a solid
element device that comprises: a solid element being flip-chip
mounted; an electric power receiving and supplying part for
receiving electric power from and supplying the electric power to
said solid element; and an inorganic sealing material for sealing
said solid element.
Further, in order to attain the above object, the invention
provides a solid element device that comprises: a solid element: an
electric power receiving and supplying part for receiving electric
power from and supplying the electric power to said solid element;
a heat resistant member for covering an electrical connection part
and a part of said electric power receiving and supplying part in
said solid element; and an inorganic sealing material for sealing
said solid element including said heat resistant member.
In order to attain the above object, the invention provides a solid
element device that comprises: a solid element; an electric power
receiving and supplying part for receiving electric power from and
supplying the electric power to said solid element; and a glass
sealing part for sealing said solid element, said glass sealing
part comprising a low melting glass selected from
SiO.sub.2--Nb.sub.2O.sub.5-based, B.sub.2O.sub.3--F-based,
P.sub.2O.sub.5--F-based, P.sub.2O.sub.5--ZnO-based,
SiO.sub.2--B.sub.2O.sub.3--La.sub.2O.sub.3-based and
SiO.sub.2--B.sub.2O.sub.3-based low melting glasses.
Furthermore, in order to attain the above object, the invention
provides a solid element device that comprises: a solid element; a
lead part made of a metal for receiving electric power from and
supplying the electric power to said solid element; and an
inorganic sealing material for sealing said solid element.
Furthermore, in order to attain the above object, the invention
provides a solid element device that comprises: a solid element; an
electric power receiving and supplying part comprising an inorganic
material substrate for receiving electric power from and supplying
the electric power to said solid element; and an inorganic sealing
material for sealing said solid element and a part of said electric
power receiving and supplying part, said inorganic sealing material
having a coefficient of thermal expansion equivalent to said
inorganic material substrate.
Furthermore, in order to attain the above object, the invention
provides a method of making a solid element device that comprises:
a mounting step of mounting a solid element on an electric power
receiving and supplying part; and a sealing step of pressing an
inorganic sealing material for said solid element in an oxygen
barrier atmosphere at a temperature at or above the deformation
point of said inorganic sealing material to perform sealing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a luminescent device in a first embodiment of the
invention, wherein (a) is a longitudinal sectional view of the
luminescent device and (b) a side view of a GaN-based LED element
as a light source;
FIG. 2 is a first variant of the luminescent device in a first
embodiment, wherein (a) is a longitudinal sectional view of the
luminescent device and (b) a side view of a GaN-based LED element
as a light source;
FIG. 3 is a longitudinal sectional view of a luminescent device
using another underfilling as a third variant;
FIG. 4 is a longitudinal sectional view of a luminescent device
provided with a mold part made of a resin material as a fourth
variant;
FIG. 5 is a longitudinal sectional view of a luminescent device in
a second embodiment;
FIG. 6 is a longitudinal sectional view of a luminescent device in
a third embodiment of the invention;
FIG. 7 is a longitudinal sectional view of a variant of the
luminescent device in the third embodiment;
FIG. 8 is a longitudinal sectional view of a luminescent device in
a fourth embodiment;
FIG. 9 is a longitudinal sectional view of a first variant of a
luminescent device in a fourth embodiment;
FIG. 10 is a longitudinal sectional view of a second variant of the
luminescent device in the fourth embodiment;
FIG. 11 is a diagram showing a luminescent device in a fifth
embodiment, wherein (a) is a plan view of the luminescent device,
(b) a side view of the luminescent device, and (c) a bottom view of
the luminescent device;
FIG. 12 is a longitudinal sectional view of a first variant of the
luminescent device in the fifth embodiment;
FIG. 13 is a longitudinal sectional view of a second variant of the
luminescent device in the fifth embodiment;
FIG. 14 is a cross-sectional view of a luminescent device in a
sixth embodiment;
FIG. 15 is a diagram showing a first variant of the luminescent
device in the sixth embodiment, wherein (a) is a longitudinal
sectional view of the luminescent device and (b) a side view of a
GaN-based LED element as a light source;
FIG. 16 is a diagram showing a second variant of the luminescent
device in the sixth embodiment, wherein (a) is a longitudinal
sectional view of the luminescent device and (b) a side view of a
GaN-based LED element as a light source;
FIG. 17 is a diagram showing a luminescent device in a seventh
embodiment, wherein (a) is a longitudinal sectional view of the
luminescent device and (b) a side view of a GaN-based LED element
as a light source;
FIG. 18 is a longitudinal sectional view of a first variant of the
luminescent device in the seventh embodiment;
FIG. 19 is a diagram showing a luminescent device in an eighth
embodiment, wherein (a) is a longitudinal sectional view of the
luminescent device and (b) a side view of a GaN-based LED element
as a light source;
FIG. 20 is a longitudinal sectional view of a variant of the
luminescent device in the eighth embodiment;
FIGS. 21 (a) to (f) are a diagram showing a formation process for
the formation of a circuit pattern with an Au layer on an AlN
substrate;
FIG. 22 is a longitudinal sectional view of a luminescent device in
a ninth embodiment;
FIG. 23 is a diagram illustrating the state of glass sealing of a
lead frame based on hot pressing;
FIG. 24 is a diagram illustrating the state of a GaN-based LED
element 2 loaded on a Si submount which functions as a Zener
diode;
FIG. 25 is a diagram showing a luminescent device in a tenth
embodiment, wherein (a) is a plan view, (b) a cross-sectional view
taken on line A-A of (a), and (c) a perspective view of lower
glass;
FIG. 26 is a cross-sectional view of a first variant of the
luminescent device in the tenth embodiment;
FIG. 27 is a cross-sectional view of a second variant of the
luminescent device in the tenth embodiment;
FIG. 28 is a diagram showing a luminescent device in an eleventh
embodiment, wherein (a) is a side view and (b) a perspective view
illustrating glass sealing;
FIG. 29 is a longitudinal sectional view of a luminescent device in
a twelfth embodiment;
FIG. 30 is a cross-sectional view showing the construction of a
face up-type light emitting element used in a working example of
the invention;
FIG. 31 is a perspective view showing an assembly of a light
emitting element and a lead;
FIG. 32 is a cross-sectional view showing a method for
manufacturing an optical device;
FIG. 33 is a cross-sectional view of an optical device in a working
example;
FIG. 34 is a cross-sectional view of an optical device in another
working example;
FIG. 35 is a cross-sectional view of an optical device in still
another working example;
FIG. 36 is a cross-sectional view of an optical device in a further
working example;
FIG. 37 is a perspective view illustrating a method for
manufacturing an optical device;
FIG. 38 is a cross-sectional view of an optical device in another
working example;
FIG. 39 is a cross-sectional view of an optical device in still
another working example;
FIG. 40 is a cross-sectional view illustrating a method for
manufacturing an optical device;
FIG. 41 is a cross-sectional view showing the construction of a
flip chip-type light emitting element;
FIG. 42 is a cross-sectional view showing an example of an optical
device using a light emitting element;
FIG. 43 is a cross-sectional view of an optical device in another
working example;
FIG. 44 is a cross-sectional view of an optical device in still
another working example;
FIG. 45 is a cross-sectional view of an optical device in a further
working example;
FIG. 46 is a cross-sectional view of an optical device in another
working example;
FIG. 47 is a plan view showing another embodiment of an assembly of
a flip chip-type light emitting element and electric power
receiving and supplying means;
FIG. 48 is a cross-sectional view of an example of an optical
device comprising an assembly;
FIG. 49 is a cross-sectional view of an optical device in another
working example;
FIG. 50 is a cross-sectional view of an optical device in still
another working example;
FIG. 51 is a cross-sectional view of an optical device in a further
working example;
FIG. 52 is a cross-sectional view of an optical device in another
working example;
FIG. 53 is a cross-sectional view of an optical device in still
another working example;
FIG. 54 is a cross-sectional view of an optical device in a further
working example;
FIG. 55 is a plan view of an optical device in another working
example;
FIG. 56 is a cross-sectional view showing a structure of an optical
element;
FIG. 57 is a diagram illustrating a method for manufacturing an
optical device in Example 10;
FIG. 58 is a diagram illustrating the state of mounting of an
optical element on a substrate;
FIG. 59 is a diagram showing the construction of an optical device
in Example 10;
FIG. 60 is a plan view showing the construction of an optical
device in another working example;
FIG. 61 is a cross-sectional view taken on line B-B of FIG. 60;
FIG. 62 is a cross-sectional view taken on line C-C (arrow tipped)
of FIG. 61;
FIG. 63 is a bottom view;
FIG. 64 is a plan view of an optical device in another working
example;
FIG. 65 is a cross-sectional view showing a structure of an optical
element in a working example;
FIG. 66 is a plan view of an optical device in Example 12;
FIG. 67 is a cross-sectional view taken on line III-III of FIG.
66;
FIG. 68 is an enlarged view of the principal part of FIG. 67;
FIG. 69 is a bottom view of an optical device in a working
example;
FIG. 70 is a diagram showing the construction of an optical device
in another working example;
FIG. 71 is a diagram showing the construction of an optical device
in still another working example;
FIG. 72 is a diagram showing the construction of an optical device
in another working example;
FIG. 73 is a diagram showing the construction of an optical device
in still another working example;
FIG. 74 is a diagram showing the construction of an optical device
in a further working example;
FIG. 75 is a cross-sectional view showing the construction of a
light emitting element;
FIG. 76 is a diagram showing the construction of a luminescent
device in a working example, wherein (A) is a cross-sectional view
and (B) a plan view;
FIG. 77 is a cross-sectional view showing the construction of a
luminescent device in a working example provided with a sealing
member;
FIG. 78 is a cross-sectional view showing the construction of a
luminescent device in a working example provided with a sealing
member in another embodiment;
FIG. 79 is a cross-sectional view showing a lead frame in another
embodiment;
FIG. 80 is a plan view showing a lead frame in still another
embodiment;
FIG. 81 is a plan view showing a lead frame in a further
embodiment;
FIG. 82 is a perspective view showing a lead frame in a still
further embodiment;
FIG. 83 is a perspective view showing a lead frame in another
embodiment;
FIG. 84 is a cross-sectional view showing the construction of a
luminescent device in a thirteenth embodiment;
FIG. 85 is a cross-sectional view showing a variant of a
luminescent device in the thirteenth embodiment;
FIG. 86 is a cross-sectional view showing a luminescent device in a
fourteenth embodiment;
FIG. 87 is a cross-sectional view showing the construction of a
luminescent device in a fifteenth embodiment;
FIG. 88 is a cross-sectional view showing the construction of a
luminescent device in a sixteenth embodiment;
FIG. 89 is a cross-sectional view showing the construction of a
luminescent device in a seventeenth embodiment;
FIG. 90 is a cross-sectional view showing the construction of a
luminescent device in an eighteenth embodiment;
FIG. 91 is a cross-sectional view showing the construction of a
luminescent device in a nineteenth embodiment;
FIG. 92 is a plan view showing a bump formed face of an LED element
of a standard size;
FIG. 93 is a plan view showing a bump formed face of an LED element
of a large size;
FIG. 94 is a cross-sectional view showing the construction of a
luminescent device in a twentieth embodiment;
FIG. 95 is a plan view illustrating the state of mounting of a
submount on a lead frame;
FIG. 96 is a diagram illustrating the state immediately before
glass sealing using a mold;
FIG. 97 is a cross-sectional view showing a variant of a
luminescent device in the twentieth embodiment;
FIG. 98 is a cross-sectional view showing a face up-type
luminescent device in a twenty-first embodiment of the
invention;
FIG. 99 is a diagram showing a flip chip-type luminescent device in
a twenty-second embodiment, wherein (a) is a cross-sectional view
and (b) a side view as viewed from the right side face of (a);
and
FIG. 100 is a diagram showing a face up-type luminescent device in
a twenty-third embodiment, wherein (a) is a cross-sectional view
and (b) a side view as viewed from the right side face of (a).
BEST MODE FOR CARRYING OUT THE INVENTION
The solid element device according to the invention will be
explained in detail in conjunction with drawings and the like.
FIG. 1 shows a luminescent device in the first embodiment of the
invention, wherein (a) is a longitudinal sectional view of the
luminescent device and (b) a side view of a GaN-based LED element
as a light source. As shown in FIG. 1 (a), this luminescent device
1 includes a flip chip-type GaN-based LED element 2, a
glass-containing Al.sub.2O.sub.3 substrate 3 with a GaN-based LED
element 2 mounted thereon, a circuit pattern 4, which is made of
tungsten (W)-nickel (Ni)-gold (Au) and is formed on the
glass-containing Al.sub.2O.sub.3 substrate 3, an Au stud bump 5 for
electrically connecting the GaN-based LED element 2 to the circuit
pattern 4, and a P.sub.2O.sub.5--ZnO-based glass sealing part 6
which seals the GaN-based LED element 2 and is bonded to the
glass-containing Al.sub.2O.sub.3 substrate 3.
As shown in FIG. 1 (b), the GaN-based LED element 2 is formed by
successive crystal growth of a buffer layer 21, an n-type layer 22,
a layer 23 including a light emitting layer, and a p-type layer 24
on the surface of a sapphire (Al.sub.2O.sub.3) substrate 20. The
GaN-based LED element 2 includes a p-electrode 25 provided on the
surface of the p-type layer 24 and an n-electrode 26 on the n-type
layer 22 exposed by removing, through etching, a part from the
p-type layer 24 to a part of the n-type layer 22. In this GaN-based
LED element 2, epitaxial growth is carried out at 700.degree. C. or
above, and the heat resistant temperature is 600.degree. C. or
above. Therefore, the GaN-based LED element 2 is stable against the
temperature at which sealing is carried out using low melting glass
which is described later.
The p-electrode 25 also functions as a lower reflector that
reflects light emitted from the layer 23 including a light emitting
layer toward the substrate 20. The size is 0.34 mm 0.34
mm.times.0.09 mm in thickness.
The glass-containing Al.sub.2O.sub.3 substrate 3 has a coefficient
of thermal expansion of 12.3.times.10.sup.-6/.degree. C. and has
via holes 3A. The via holes 3A function to conduct the circuit
pattern 4 made of W formed by metallization of the surface and
backside of the substrate.
The glass sealing part 6 is made of P.sub.2O.sub.5--ZnO-based low
melting glass (coefficient of thermal expansion:
11.4.times.10.sup.-6/.degree. C., yield point: 415.degree. C.,
refractive index: 1.59, internal transmittance: 99% (470 nm)) and
is in a rectangular form which has an upper face 6A and a side face
6B formed based on bonding of the glass sealing part to the
glass-containing Al.sub.2O.sub.3 substrate 3 by hot pressing in a
mold followed by dicer cutting.
The low melting glass is processed at an incomparably higher
viscosity than a viscosity level which is generally regarded as a
high viscosity in resins. Further, in the case of glass, even when
the temperature exceeds the yield point by several tens of degrees,
the viscosity is not lowered to the level of the general resin
sealing. When the viscosity on a conventional resin molding level
is contemplated, a temperature above the crystal growth temperature
of the LED element is required, or deposition on the mold occurs.
This renders sealing and molding difficult. For this reason,
processing at 10.sup.6 poises or more is preferred.
The method for manufacturing this luminescent device 1 will be
explained.
At the outset, a glass-containing Al.sub.2O.sub.3 substrate 3
having via holes 3A is provided. A W paste is screen printed on the
surface of the glass-containing Al.sub.2O.sub.3 substrate 3
according to the circuit pattern. Next, the W paste printed
glass-containing Al.sub.2O.sub.3 substrate 3 is heat treated at a
temperature above 1000.degree. C. to bake W to the substrate 3.
Further, Ni plating and Au plating are provided on W to form the
circuit pattern 4. Next, the GaN-based LED element 2 is
electrically connected to the circuit pattern 4 (surface side) in
the glass-containing Al.sub.2O.sub.3 substrate 3 through Au stud
bumps 5. Next, a P.sub.2O.sub.5--ZnO-based low melting glass sheet
is set parallel to the glass-containing Al.sub.2O.sub.3 substrate 3
with the GaN-based LED element 2 mounted thereon, and, in a
nitrogen atmosphere, the pressure is brought to 60 kgf followed by
hot pressing at a temperature of 465.degree. C. The viscosity of
the low melting glass under the above conditions is 10.sup.8 to
10.sup.9 poises, and the low melting glass is bonded to the
glass-containing Al.sub.2O.sub.3 substrate 3 through an oxide
contained therein. The glass-containing Al.sub.2O.sub.3 substrate 3
integrated with the low melting glass is then set in a dicer for
dicing to isolate the rectangular luminescent device 1.
The following effects can be attained by the first embodiment. (1)
Processing at a temperature satisfactorily below the crystal growth
temperature can be realized by using low melting glass and hot
pressing in a highly viscous state. (2) High sealing strength can
be provided by bonding the glass-containing Al.sub.2O.sub.3
substrate 3 to the glass sealing part 6 by a chemical bond through
an oxide. Therefore, even a small package having a small bonding
area can be realized. (3) The coefficient of thermal expansion of
the sealing glass is similar to the coefficient of thermal
expansion of the glass-containing Al.sub.2O.sub.3 substrate.
Therefore, bringing the temperature to room temperature or low
temperature after bonding at a high temperature, a bonding failure
such as separation or cracking is less likely to occur. Further,
glass is not cracked upon exposure to tensile stress, and cracking
is less likely to occur upon exposure to compressive stress. The
coefficient of thermal expansion of the sealing glass is somewhat
lower than that of the glass-containing Al.sub.2O.sub.3 substrate.
According to an experiment conducted by the present inventor,
neither separation nor cracking occurs in a 1000-cycle liquid phase
thermal shock test of -40.degree. C..revreaction.100.degree. C.
Further, the present inventor has conducted a basic confirmation
experiment of bonding a glass piece having a size of 5 mm.times.5
mm to a ceramic substrate. As a result, in a combination of various
coefficients of thermal expansion for both glass and ceramic
substrates, when the thermal expansion coefficient ratio of the
member having a lower coefficient of thermal expansion to the
member having a higher coefficient of thermal expansion is not less
than 0.85, crack-free bonding could be realized. The similar
coefficient of thermal expansion means a thermal expansion
coefficient difference in the above range, although this depends
upon the rigidity and size of the member, or the stress absorbing
layer in the eighth embodiment and the like. (4) Flip chip bonding
can eliminate the need to use any wire. Therefore, any trouble does
not occur in electrodes even in the case of processing in a highly
viscose state. The low melting glass during sealing is hard and has
a viscosity of 10.sup.8 to 10.sup.9 poises. On the other hand, the
epoxy resin before heat curing is liquid and has a viscosity of
about 5 poises. Thus, they are greatly different from each other in
physical properties. Accordingly, unlike sealing of the face
up-type LED element in which the electrode on the element surface
is electrically connected to an electric power supplying member
such as a lead through a wire, it is possible to prevent such an
unfavorable phenomenon that the wire is collapsed or deformed
during glass sealing. Further, unlike sealing of the flip chip-type
LED element in which the electrode on the surface of the element is
subjected to flip chip bonding to an electric power supplying
member such as a lead through a bump such as gold (Au), it is
possible to prevent such an unfavorable phenomenon that, upon
application of pressure to the LED element in its electric power
supplying member direction based on the viscosity of the glass,
collapse of the bump or short-circuiting between bumps occurs. (5)
When the low melting glass and the glass-containing Al.sub.2O.sub.3
substrate 3 are set parallel to each other followed by hot pressing
in a highly viscose state, the low melting glass is parallely moved
on and brought to intimate contact with the surface of the
glass-containing Al.sub.2O.sub.3 substrate to seal the GaN-based
LED element 2. Therefore, no void occurs. (6) The circuit pattern 4
for wiring of the glass-containing Al.sub.2O.sub.3 substrate 3 is
drawn to the backside through the via holes 3A. Therefore, a
plurality of luminescent devises 1 can easily be mass-produced
based on dicer cutting by simply subjecting a plurality of devices
to sealing at a time with a low melting glass sheet without the
need to take any special measure for preventing unfavorable
phenomena such as the entry of glass into unnecessary places and
covering electric terminals with the glass. The low melting glass
is processed in a highly viscose state. Therefore, unlike the case
of resin, there is no need to take a sufficient measure, and
drawing of an external terminal to the backside suffices for coping
with mass production without relying upon via holes. (7) Flip chip
mounting of the GaN-based LED element 2 can overcome problems
involved in the realization of glass sealing and, at the same time,
has the effect of realizing a micro-luminescent device 1 having a
size of 0.5 mm square. These effects can be attained by virtue of
unnecessary wire bonding space, the selection of the member for the
glass sealing part 6 and the member for the glass-containing
Al.sub.2O.sub.3 substrate 3 which are equal to each other in
coefficient of thermal expansion and strong bonding based on a
chemical bond which can prevent interfacial peeling even in the
case of bonding in a small space.
FIG. 2 shows a first variant of a luminescent device in the first
embodiment, wherein (a) is a longitudinal sectional view of the
luminescent device and (b) a side view of the GaN-based LED element
as a light source. In the following explanation, common constituent
parts are identified with the same reference numerals.
This luminescent device 1 is different from the first embodiment in
that a face up-type GaN-based LED element 2 is connected to a
circuit pattern 4 by flip chip boding and, in addition, a white
underfilling 7 is provided for protecting the GaN-based LED element
2 in its electrode and the Au stud bump 5.
The underfilling 7 may be composed of a filling material with a
good light reflectivity such as boron nitride (BN) and is provided
by previously potting the material in a glass-containing
Al.sub.2O.sub.3 substrate 3 before bonding of the GaN-based LED
element 2 and conducting flip chip bonding of the GaN-based LED
element 2 onto the underfilling.
As shown in FIG. 2 (b), the GaN-based LED element 2 includes a
light transparent electrode 27 such as ITO (indium tin oxide)
provided on a surface of a p-type layer 24, and a p-electrode 25
provided on a surface of the light transparent electrode 27.
In the first variant, even in the case of the face up-type
GaN-based LED element 2, light reflected and diffused by the
underfilling 7 is radiated from the substrate 20 of the GaN-based
LED element 2, contributing to improved light takeout efficiency.
In the second embodiment, the white underfilling 7 is selected for
enhancing the light takeout efficiency. When the light takeout
efficiency is immaterial, underfilling 7 having a color other than
the white color may be used.
In the second variant, the surface of the glass sealing part 6 may
be treated for improving the moisture resistance, resistance to
acids and alkalis. In this case, surface treatment with MgF.sub.2,
SiO.sub.2, or SiN is effective. Treatment for reducing interfacial
reflection may also be carried out, for example, by antireflective
multilayered film or the like. In this case, multilayered coating
of TiO.sub.2+SiO.sub.2 is effective.
FIG. 3 is a longitudinal sectional view of another luminescent
device using underfilling as a third variant. In the luminescent
device 1 in the third variant, diamond which is highly thermally
conductive is used as the underfilling 7 for protecting the
electrode of the GaN-based LED element 2 and the Au stud bumps 5.
Other examples of highly thermally conductive underfilling 7
include BN, aluminum nitride (AlN), and silicon carbide (SiC). They
are used as a filling material with an average particle diameter of
a few microns to be mixed into a heat resistant ceramic coating
material.
FIG. 4 is a longitudinal sectional view of a luminescent device
provided with a mold part made of a resin material as a fourth
variant. In this luminescent device 1, the luminescent device 1
explained in the first embodiment is bonded to a lead frame 8, and,
further, a mold part 9 the whole of which is made of an epoxy resin
is provided.
The mold part 9 is provided with a semispherical optical shape face
9A formed by transfer molding.
According to this construction, an optical system can be easily
formed in a glass sealing-type device, and, at the same time, the
moisture resistance is further improved by surrounding the
glass-containing Al.sub.2O.sub.3 substrate 3 and the glass sealing
part 6 by the mold part 9. The mold part 9 may be made of a resin
material other than the epoxy resin, for example, silicone resin. A
molding technique other than the transfer molding, for example,
potting molding may also be applied. The mold part may also be
formed by an injection method using a resin material such as an
acrylic resin or polycarbonate, and, in this case, the productivity
can be improved.
Further, a phosphor may be incorporated in the mold part 9. The
phosphor may be, for example, a YAG phosphor, a silicate phosphor,
or a mixture of the YAG phosphor and the silicate phosphor at a
predetermined ratio.
FIG. 5 is a longitudinal sectional view of a luminescent device in
the second embodiment. This luminescent device 1 is different from
the device in the first embodiment in that an
SiO.sub.2--Nb.sub.2O.sub.5-based glass sealing part 6 is provided
instead of the glass material used in the luminescent device 1 in
the first embodiment, and an Ag-based circuit pattern 4 is provided
in the glass-containing Al.sub.2O.sub.3 substrate 3.
The SiO.sub.2--Nb.sub.2O.sub.5-based glass sealing part 6 is made
of SiO.sub.2--Nb.sub.2O.sub.5-based low melting glass (coefficient
of thermal expansion: 12.1.times.10.sup.-6/.degree. C., yield
point: 507.degree. C., refractive index: 1.69, internal
transmittance: 98% (470 nm)), and is molded into a rectangular form
which has an upper face 6A and a side face 6B formed based on
bonding of the glass sealing part to the glass-containing
Al.sub.2O.sub.3 substrate 3 by hot pressing in a mold followed by
dicer cutting.
The glass-containing Al.sub.2O.sub.3 substrate 3 has a coefficient
of thermal expansion: 12.3.times.10.sup.-6/.degree. C. and has via
holes 3A. These via holes 3A are provided for continuity of an Ag
circuit pattern 4 by electroplating on the surface and backside of
the substrate.
In the second embodiment, the use of the
SiO.sub.2--Nb.sub.2O.sub.5-based low melting glass can reduce
moisture permeability and can improve light takeout efficiency.
Further, when the low melting glass having small moisture
permeability is used, Ag, a highly reflective material, can be used
even in the case where voltage is applied as in a circuit pattern
in conducting flip chip mounting of a GaN-based LED element 2 or
the like, and resin sealing is difficult due to a fear of migration
as in the case of pattern spacing of a few tens of microns.
FIG. 6 is a longitudinal sectional view of a luminescent device in
the third embodiment of the invention. This luminescent device 1
includes a face up-type GaN-based LED element 2, a glass-containing
Al.sub.2O.sub.3 substrate 3 with the GaN-based LED element 2
mounted thereon, a circuit pattern 4 provided on the
glass-containing Al.sub.2O.sub.3 substrate 3 made of W, an Au stud
bump 5 for electrically connecting the GaN-based LED element 2 to a
circuit pattern 4, a wire 10 made of Au for electrically connecting
the GaN-based LED element 2 in its electrode to the circuit pattern
4, a heat resistant inorganic material coating 11 for surrounding
and coating the GaN-based LED element 2, the wire 10, and the
circuit pattern 4, an inorganic white adhesive 12 for binding the
GaN-based LED element 2 to the circuit pattern 4, and a
P.sub.2O.sub.5--ZnO-based glass sealing part 6 for sealing and
bonding to the glass-containing Al.sub.2O.sub.3 substrate 3.
The heat resistant inorganic material coating 11 is a light
transparent and porous SiO.sub.2-based hard coating and functions
to prevent deformation of the wire 10 in sealing of
P.sub.2O.sub.5--ZnO-based glass.
The inorganic white adhesive 12 reflects light emitted from the
GaN-based LED element 2 toward the substrate side and radiates the
light from the electrode formed face.
The method for manufacturing this luminescent device 1 will be
explained.
A glass-containing Al.sub.2O.sub.3 substrate 3 with via holes 3A is
first provided. A W paste is screen printed on the surface of the
glass-containing Al.sub.2O.sub.3 substrate 3 according to the
circuit pattern. Next, the glass-containing Al.sub.2O.sub.3
substrate 3 with the W paste printed thereon is heat treated at
1500.degree. C. to bake W to the substrate 3. Further, an Ni
plating or an Au plating is provided on W to form a circuit pattern
4. Next, a GaN-based LED element 2 is bonded to the circuit pattern
4 (surface, side) in the glass-containing Al.sub.2O.sub.3 substrate
3 with the aid of an inorganic white adhesive 12. The GaN-based LED
element 2 in its p-electrode and n-electrode is then electrically
connected to the circuit pattern 4 through a wire 10. A
SiO.sub.2-based coating material is then potted so as to surround
the GaN-based LED element 2 and the wire 10. The assembly is then
heat treated at 150.degree. C. to form a porous heat resistant
inorganic material coating 11. Next, a P.sub.2O.sub.5--ZnO-based
low melting glass is set parallel to the glass-containing
Al.sub.2O.sub.3 substrate 3 with the GaN-based LED element 2
mounted thereon, and the assembly is hot pressed under conditions
of pressure 60 kgf and temperature 415.degree. C. or above. The
glass-containing Al.sub.2O.sub.3 substrate 3 integrated with the
low melting glass is then set in a dicer followed by dicing to
isolate rectangular luminescent devices 1.
In the third embodiment, a light transparent heat resistant
inorganic material coating 11 is provided on the wire 10.
Therefore, glass sealing of the wire bonded GaN-based LED element 2
with the P.sub.2O.sub.5--ZnO-based low melting glass is possible in
high yield and, thus, a glass sealing-type luminescent device 1 can
be realized.
The glass sealing can be realized without the provision of the heat
resistant inorganic material coating 11. In this case, however,
deformation of the wire 10 is unavoidable. Therefore, electrical
short-circuiting is likely to occur, and the yield is lowered.
Further, the ball-shaped bonded part of the Au wire 10 is collapsed
on the GaN-based LED element 2. Therefore, disadvantageously,
electrical short-circuiting is likely to occur, and, further,
problems such as covering of an Au film on the surface of the
element, resulting in inhibition of takeout of light.
FIG. 7 is a longitudinal cross-sectional view showing a variant of
the luminescent device in the third embodiment. This luminescent
device 1 is different from the device in the third embodiment in
that an AlInGaP-based LED element 2 having an-electrode on its
upper and lower parts.
In the AlInGaP-based LED element 2, the upper electrode is
electrically connected to the circuit pattern 4 through a wire 10,
and the lower electrode is electrically connected to the circuit
pattern 4 through an Ag paste 13.
Thus, also in the LED element with an-electrode provided on its
upper and lower surfaces, a glass sealing-type luminescent device 1
can be realized in a high yield by applying a heat resistant
inorganic material coating 11 and conducting glass sealing with
P.sub.2O.sub.5--ZnO-based low melting glass.
FIG. 8 is a longitudinal sectional view showing a luminescent
device in the fourth embodiment. This luminescent device 1 is
different from the device in the luminescent device 1 in the first
embodiment in that the GaN-based LED element 2 has been formed
based on scribing. The GaN-based LED element 2 formed based on
scribing has a sharp concave-convex on its side face as the cut
part, and, thus, the side face is covered by an element coating
material 14.
The element coating material 14 may be, for example, an
SiO.sub.2-based coating material. The SiO.sub.2-based coating
material is coated so as to cover the side face of the GaN-based
LED element 2, and the coating is heat treated at 150.degree. C.
for curing.
In the fourth embodiment, the sharp concave-convex part formed in
the GaN-based LED element 2 by scribing is likely to be a starting
point of cracking and is causative of void formation. Therefore,
covering of the concave-convex part with the element coating
material 14 for smoothing can prevent cracking. Further, void
formation can also be prevented.
FIG. 9 is a longitudinal sectional view showing a first variant of
the luminescent device in the fourth embodiment. This luminescent
device 1 is different from the device in the fourth embodiment in
that the element coating material 14 made of a SiO.sub.2-based
coating material is provided so as to cover the whole periphery of
the GaN-based LED element 2.
The element coating material 14 has a coefficient of thermal
expansion intermediate between the coefficient of thermal expansion
of the GaN-based LED element 2 and the coefficient of thermal
expansion of the P.sub.2O.sub.5--ZnO-based low melting glass. The
above-defined coefficient of thermal expansion of the element
coating material 14 can prevent cracking, for example, even when
glass having a large coefficient of thermal expansion is used or a
large-size LED element is used.
In the first variant, cracking and void formation caused by the
shape of the surface of the GaN-based LED element 2 can be
suppressed, and, further, cracking derived from the difference in
coefficient of thermal expansion between the GaN-based LED element
2 and the low melting glass can be prevented. When the efficiency
of takeout of light emitted from the GaN-based LED element 2 is
taken into consideration, the thickness of the element coating
material 14 is preferably as small as possible.
FIG. 10 is a longitudinal sectional view showing a second variant
of the luminescent device in the fourth embodiment. This
luminescent device 1 is different from the device in the fourth
embodiment in that a phosphor-containing phosphor layer 15 is
provided so as to cover the whole periphery of the GaN-based LED
element 2.
The phosphor layer 15 comprises a YAG-based phosphor as a phosphor
mixed in the element coating material 14 made of a SiO.sub.2-based
coating material used in the first variant. A single type of
phosphor or plural types of phosphors may be mixed in the element
coating material 14. Other phosphors usable herein include silicate
phosphors. Further, a mixture of the YAG-based phosphor with the
silicate phosphor may be contained in the phosphor layer 15.
In the second variant, in addition to the favorable effects of the
first variant, an additional effect can be attained. Specifically,
since the phosphor is shielded from external moisture by glass
sealing, a deterioration of the phosphor can be prevented, and
stable wavelength conversion can be realized for a long period of
time.
FIG. 11 shows a luminescent device in the fifth embodiment, wherein
(a) is a plan view of the luminescent device, (b) a side view of
the luminescent device, and (c) a bottom view of the luminescent
device. This luminescent device 1 includes a plurality of flip
chip-type GaN-based LED elements 2, a squarely formed
glass-containing Al.sub.2O.sub.3 substrate 3 having a multilayered
structure with the GaN-based LED elements 2 mounted thereon, a
circuit pattern 4, made of tungsten (W) provided on the surface of
the glass-containing Al.sub.2O.sub.3 substrate 3 and within the
layers (an Ni, Au plating being further applied on the pattern on
the substrate surface), an Au stud bump 5 for electrically
connecting the GaN-based LED element 2 to the circuit pattern 4, a
P.sub.2O.sub.5--ZnO-based glass sealing part 6 for sealing of the
GaN-based LED element 2 and, in addition, bonding to the
glass-containing Al.sub.2O.sub.3 substrate 3, bottom circuit
patterns 16A (anode), 16C (cathode) exposed from in-layer
intermediate layer at four corners of the glass-containing
Al.sub.2O.sub.3 substrate 3, and a heat dissipation pattern 17 made
of a copper foil for dissipating heat based on heat generation of
the GaN-based LED element 2 into the exterior of the assembly. In
this case, nine in total of GaN-based LED elements 2 are arrayed
(3.times.3) on the circuit pattern 4 patterned on the substrate
surface so as to have a circular outer shape through the Au stud
bump 5.
The glass-containing Al.sub.2O.sub.3 substrate 3 has a multilayered
structure with in-layer wiring made of W, and, three GaN-based LED
elements 2 in a column-wise direction shown in FIG. 11 (b) are
connected in series to form an element group. The anode in the
element group is connected to one of the bottom circuit patterns
16A, and the cathode in the element group is connected to the
bottom circuit pattern 16C. Further, to, the cathode is connected
the cathode in element groups formed for other two columns.
In the fifth embodiment, also when a plurality of GaN-based LED
elements 2 are used, a series/parallel circuit can easily be formed
by using a ceramic multilayered substrate, and, further, in
electroplating, drawing of the wiring is also easy. Rapid thermal
conduction of heat, produced based on light emission from densely
mounted nine GaN-based LED elements 2, from the heat dissipation
metal pattern to a heat sink or the like can be realized by drawing
an external electrical connection terminal from the intermediate
layer and providing a metal pattern for heat dissipation on the
bottom face.
FIG. 12 is a longitudinal sectional view showing a first variant of
the luminescent device in the fifth embodiment. This luminescent
device 1 is different from the device in the fifth embodiment in
that a phosphor layer 15 is provided on the surface of the
P.sub.2O.sub.5--ZnO-based glass sealing part 6 to constitute a
wavelength conversion-type luminescent device 1.
In the first variant, the provision of the phosphor layer 15
surrounding the whole GaN-based LED element 2 in the
P.sub.2O.sub.5--ZnO-based glass sealing part 6 can realize a
high-light output white luminescent device 1. Further, even though
there is a variation in individual LED element characteristics in
the multi-element-type luminescent device 1, the difference is less
likely to be conspicuous and, thus, a luminescent device 1 having
uniform luminescent characteristics can be realized.
FIG. 13 is a longitudinal sectional view showing a second variant
of the luminescent device in the fifth embodiment. This luminescent
device 1 is different from the device in the fifth embodiment in
that a blue or green light emitting flip chip-type GaN-based LED
element 2 and a red light emitting upper/lower electrode-type
AlInGaP-based LED element 2 are provided together followed by
sealing by a P.sub.2O.sub.5--ZnO-based glass sealing part 6. The
AlInGaP-based LED element 2, together with the wire 10, is
surrounded by the heat resistant inorganic material coating 11.
In the second variant, even when the flip chip-type LED element and
the upper/lower electrode-type LED element are provided together,
glass sealing by the P.sub.2O.sub.5--ZnO-based low melting glass is
possible. A combination of luminescent colors of the LED elements 2
may also be desirably set.
FIG. 14 is a cross-sectional view of a luminescent device in the
sixth embodiment. This luminescent device 1 includes an
AlInGaP-based LED element 2 having an-electrode on its upper and
lower parts, a glass-containing Al.sub.2O.sub.3 substrate 3 with
the AlInGaP-based LED element 2 mounted thereon, a circuit pattern
4 formed on the glass-containing Al.sub.2O.sub.3 substrate 3 made
of W, an Au wire 10 for electrically connecting the AlInGaP-based
LED element 2 in its electrode to the circuit pattern 4, a high
refractive index material coating 11A of TiO.sub.2 (refractive
index: 2.4) for surrounding and coating the AlInGaP-based LED
element 2, the wire 10, and the circuit pattern 4, an Ag paste 13
for bonding and electrically connecting the AlInGaP-based LED
element 2 to the circuit pattern 4, and an
SiO.sub.2--Nb.sub.2O.sub.5-based glass sealing part 6 for sealing
the AlInGaP-based LED element 2 and bonded to glass-containing
Al.sub.2O.sub.3 substrate 3.
The SiO.sub.2--Nb.sub.2O.sub.5-based glass sealing part 6 is made
of SiO.sub.2--Nb.sub.2O.sub.5-based low melting glass (coefficient
of thermal expansion: 10.2.times.10.sup.-6/.degree. C., yield
point: 543.degree. C., refractive index: 1.92, internal
transmittance: 81% (470 nm), 91% (520 nm (in thickness 10 mm))) and
has a semisphericl optical shape face 6D. In this
SiO.sub.2--Nb.sub.2O.sub.5-based glass sealing part 6, light, which
is emitted from the AlInGaP-based LED element 2, is passed through
the high refractive index material coating 11A and reaches this
sealing part 6, enters the glass interface substantially
perpendicularly to minimize interface reflection and is radiated to
the exterior of the assembly. The optical shape face 6D may be of a
form other than the semisphere so far as light emitted from the
AlInGaP-based LED element 2 enters at a critical angle or less to
the interface of the glass sealing part 6. Specifically, the
optical shape face 6D may be in a hexahedron or octahedron
form.
In the sixth embodiment, the AlInGaP-based LED element 2 is
surrounded by the high refractive index material coating 11A made
of TiO.sub.2 with a refractive index of 2.4 and is sealed by the
SiO.sub.2--Nb.sub.2O.sub.5-based glass sealing part 6 having a
refractive index of 1.92. Therefore, the occurrence of interface
reflection loss at the interface of the high refractive index
material coating 11A and the SiO.sub.2--Nb.sub.2O.sub.5-based glass
sealing part 6 can be suppressed, and the efficiency of takeout of
light from the LED element as the high refractive index medium can
be improved.
Further, since the SiO.sub.2--Nb.sub.2O.sub.5-based glass sealing
part 6 is formed in a convex form, light emitted from the
AlInGaP-based LED element 2 enters the interface of the glass
sealing part 6 and the air at an angle corresponding to near
vertical incidence, resulting in enhanced external radiation
efficiency.
FIG. 15 shows a first variant of the luminescent device in the
sixth embodiment, wherein (a) is a longitudinal sectional view of
the luminescent device and (b) a side view of a GaN-based LED
element as a light source. This luminescent device 1 is different
from the device in the sixth embodiment in that a GaN-based LED
element 2 provided with an SiC substrate 29 is used instead of the
AlInGaP-based LED element 2 and, further, an optical shape face 6D
made of an SiO.sub.2 film 6E having a quarter-wavelength thickness
is provided on the surface of the SiO.sub.2--Nb.sub.2O.sub.5-based
glass sealing part 6.
The SiC substrate 29 has on its bottom face an n-electrode 26 which
is electrically connected to the circuit pattern 4 through an Ag
paste 13.
In the first variant, the provision of the SiO.sub.2 film 6E having
a quarter-wavelength thickness on the optical shape face 6D can
reduce reflection because light led to the optical shape face 6D
interferes in the SiO.sub.2 film 6E.
FIG. 16 shows a second variant of the luminescent device in the
sixth embodiment, wherein (a) is a longitudinal sectional view of
the luminescent device and (b) a side view of a GaN-based LED
element as a light source. This luminescent device 1 is different
from the device in the sixth embodiment in that a flip chip-type
GaN-based LED element 2 provided with a GaN substrate 30 is used
instead of the AlInGaP-based LED element 2.
In the second variant, by virtue of the use of the GaN-based LED
element 2 provided with the GaN substrate 30, light can be
efficiently led to the substrate surface without interface
reflection within the LED element. The light led to the surface of
the substrate is radiated to the exterior of the device from the
optical shape face 6D through the SiO.sub.2--Nb.sub.2O.sub.5-based
glass sealing part 6, whereby high external radiation efficiency
can be realized.
FIG. 17 shows a luminescent device in the seventh embodiment,
wherein (a) is a longitudinal sectional view of the luminescent
device and (b) a side view of a GaN-based LED element as a light
source. This luminescent device 1 is different from the devices in
the first to sixth embodiments in that, instead of the
glass-containing Al.sub.2O.sub.3, Al.sub.2O.sub.3 is used as the
substrate and a sealing glass material corresponding to the
coefficient of thermal expansion of Al.sub.2O.sub.3 is used. FIG.
17 illustrates the state before splitting into individual devices.
As shown in FIG. 17 (a), each of the luminescent devices 1 includes
a flip chip-type GaN-based LED element 2, an Al.sub.2O.sub.3
substrate 3 with the GaN-based LED element 2 mounted thereon, a
circuit pattern 4 provided on the Al.sub.2O.sub.3 substrate 3, an
Au stud bump 5 for electrically connecting the GaN-based LED
element 2 to the circuit pattern 4, and a B.sub.2O.sub.3--F-based
glass sealing part 6 for sealing the GaN-based LED element 2 and
bonded to the Al.sub.2O.sub.3 substrate 3.
As shown in FIG. 17 (b), in order to prevent damage to the Au stud
bump 5 in the sealing of the B.sub.2O.sub.3--F-based glass and
interelectrode short-circuiting, underfilling 7 is filled into a
part between the GaN-based LED element 2 and the Al.sub.2O.sub.3
substrate 3.
The Al.sub.2O.sub.3 substrate 3 has via holes 3A, and the circuit
pattern 4 on the surface is electrically connected to the circuit
pattern 4 on the backside through the via holes 3A. Grooves 3B as a
substrate splitting position are formed at predetermined
intervals.
In the circuit pattern 4, bonding patterns 4A, 4B for enhancing the
strength of bonding to the B.sub.2O.sub.3--F-based glass sealing
part 6 are provided on the surface on which the GaN-based LED
element 2 is to be mounted, and the bonding pattern 4B serves also
as a part of the circuit pattern 4 drawn out to the backside of the
Al.sub.2O.sub.3 substrate 3.
The B.sub.2O.sub.3--F-based glass sealing part 6 is made of
B.sub.2O.sub.3--F-based low melting glass (coefficient of thermal
expansion: 6.9.times.10.sup.-6/.degree. C., yield point:
539.degree. C., refractive index: 1.75, internal transmittance: 98%
(470 nm)) and is bonded to the surface of the Al.sub.2O.sub.3
substrate 3 by hot pressing a preform glass on which an optical
shape face 6D and a small thickness part 6B have previously been
provided by preforming. The small thickness part 6B is formed in
such a thickness that damage such as cracking does not extend to
the adjacent luminescent device 1 upon the application of a load to
scribing part for splitting.
In the luminescent device 1, after the GaN-based LED element 2 is
mounted and sealed by the B.sub.2O.sub.3--F-based glass sealing
part 6, a load is applied using the groove 3B in the
Al.sub.2O.sub.3 substrate 3 as the splitting position, whereby the
Al.sub.2O.sub.3 substrate 3 is broken based on stress concentration
and, at the same time, the B.sub.2O.sub.3--F-based glass sealing
part 6 is split at the small thickness part 6B.
In the seventh embodiment, the use of a commonly widely used
Al.sub.2O.sub.3 substrate can reduce white light absorption and can
improve light takeout efficiency. Further, the Al.sub.2O.sub.3
substrate is easily available and is inexpensive. Furthermore,
since splitting into individual luminescent devices 1 is carried
out by applying a load to the scribing part, mass productivity is
excellent. In the splitting into individual luminescent devices 1
by dicing, upon cutting by a dicer, residual stain occurs in the
glass and, consequently, cracking sometimes occurs in the
B.sub.2O.sub.3--F-based glass sealing part 6 upon exposure to heat
shock. On the other hand, in the luminescent device 1 split based
on scribing, residual strain is small and, thus, a failure such as
cracking is less likely to occur.
SiO.sub.2--B.sub.2O.sub.3--La.sub.2O.sub.3-based low melting glass
(coefficient of thermal expansion: 8.3.times.10.sup.-6/.degree. C.,
yield point: 559.degree. C., refractive index: 1.81, internal
transmittance: 99% (470 nm)) may also be used as low melting glass
other than the B.sub.2O.sub.3--F-based glass.
Regarding a splitting method other than the scribing, splitting
using a laser beam may also be adopted.
FIG. 18 is a longitudinal sectional view showing a first variant of
the luminescent device in the seventh embodiment. This luminescent
device 1 is different from the device in the seventh embodiment in
that the B.sub.2O.sub.3--F-based glass sealing part 6 is formed by
flat B.sub.2O.sub.3--F-based low melting glass.
The B.sub.2O.sub.3--F-based SiO.sub.2--B.sub.2O.sub.3 glass sealing
part 6 has a scribing part 6C at a position opposite to the groove
3B provided in the Al.sub.2O.sub.3 substrate 3, and, upon the
application of a load, the scribing part 6C cooperates with the
groove 3B to cause stress concentration, whereby the
B.sub.2O.sub.3--F-based glass sealing part 6 and the
Al.sub.2O.sub.3 substrate 3 are split.
The first variant renders the preform of the
B.sub.2O.sub.3--F-based glass sealing part 6 unnecessary to
simplify the manufacturing process, contributing to excellent
productivity.
Further, SiO.sub.2--B.sub.2O.sub.3-based low melting glass can also
be used as other low melting glass applicable to the glass sealing
part 6.
FIG. 19 is a luminescent device of the eighth embodiment, wherein
(a) is a longitudinal sectional view of the luminescent device and
(b) a side view of a GaN-based LED element as a light source. This
luminescent device 1 is different from the device in the seventh
embodiment in that this device is provided with BN underfilling 7
having excellent thermal conductivity on the lower part of the
GaN-based LED element 2, an AlN substrate 3 with the GaN-based LED
element 2 mounted thereon, and an SiO.sub.2--B.sub.2O.sub.3-based
glass sealing part 6, having a coefficient of thermal expansion
similar to AlN, for sealing the GaN-based LED element 2 and bonded
to the AlN substrate 3.
The SiO.sub.2--B.sub.2O.sub.3-based glass sealing part 6 is made of
SiO.sub.2--B.sub.2O.sub.3-based low melting glass (coefficient of
thermal expansion: 4.9.times.10.sup.-6/.degree. C., yield point:
558.degree. C., refractive index: 1.61, internal transmittance: 96%
(380 nm)) and has a coefficient of thermal expansion substantially
equal to the coefficient of thermal expansion
(5.times.10.sup.-6/.degree. C.) of the GaN-based LED element 2.
In the eighth embodiment, heat produced based on light emission
from the GaN-based LED element 2 is passed through highly thermally
conductive unerfilling 7 and Au stud bump 5, is conveyed to the AlN
substrate 3 as a high heat dissipation material and is then
efficiently dissipated to the outside of the device. Further, since
main members such as the GaN-based LED element 2, the AlN substrate
3, and the SiO.sub.2--B.sub.2O.sub.3-based glass sealing part 6 are
substantially equal to one another in coefficient of thermal
expansion, separation and deterioration in sealing properties
derived from the difference in coefficient of thermal expansion can
be prevented.
For example, even when there is a difference in coefficient of
thermal expansion between the main members, the provision of a
construction capable of relaxing the stress can absorb the internal
stress and can prevent deterioration in sealing properties and
separation.
FIG. 20 is a longitudinal sectional view showing a variant of the
luminescent device in the eighth embodiment. This luminescent
device 1 is different from the device in the seventh embodiment in
that a soft metal layer for absorbing the internal stress is
provided on the surface of the GaN-based LED element 2 mounted
circuit pattern 4.
FIGS. 21 (a) to (e) are diagrams showing a process for forming a
circuit pattern on the AlN substrate. At the outset, as shown in
(a), a W-containing paste is screen printed according to the
circuit pattern on both sides of the AlN substrate 3 with via holes
3A previously formed therein. Next, the AlN substrate 3 is sintered
at a temperature above 1500.degree. C. to bake W to the AlN
substrate 3. Thus, W is strongly bonded to the AlN substrate 3.
Alternatively, W may be formed by sputtering. Further, instead of
W, a high melting metal such as Mo may be used. Next, as shown in
(b), a nickel (Ni) layer 26 is provided by plating on the circuit
pattern 4 on the surface side of the AlN substrate 3. Next, as
shown in (c), the AlN substrate 3 is heated at about 700.degree. C.
to react Ni with W. Thus, the circuit pattern 4 is strongly bonded
onto the AlN substrate 3. Next, as shown in (d), an Au layer 4C is
formed by electroplating on the surface of the circuit pattern 4.
As shown in (e), the GaN-based LED element 2 is then mounted at a
predetermined position through an Au stud bump 5.
SiO.sub.2--B.sub.2O.sub.3-based low melting glass is hot pressed on
the AlN substrate 3 with the GaN-based LED element 2 mounted on the
circuit pattern 4, followed by splitting into individual
luminescent devices 1 based on scribing.
In the above variant, the strong circuit pattern 4 can be bonded to
the AlN substrate 3. Further, the provision of the Au pattern 4C
for mounting the GaN-based LED element 2 on the circuit pattern 4
through the Au stud bump and the provision of the Ni pattern 4A for
bonding to the low melting glass can realize stud bump mounting
and, at the same time, can relax stress. In the glass, bonding is
carried out through an oxide, and bonding to Au does not occur, but
on the other hand, bonding to Ni takes place through an Ni oxide
film on the Ni surface. Further, good bonding can also be realized
between the glass and AlN. The thermal conductivity of the AlN
substrate is so high that a difference in temperature between the
AlN substrate and the glass is likely to occur, for example,
immediately after lighting of the GaN-based LED element 2. Even in
such a situation, stable glass sealing properties can be realized
as a result of stress relaxation based on the elastic deformation
of the Au layer 4C can be provided.
FIG. 22 is a longitudinal sectional view of a luminescent device in
the ninth embodiment. This luminescent device 1 includes a flip
chip-type GaN-based LED element 2, an AlN submount 18 on which the
GaN-based LED element 2 is mounted, a W circuit pattern 4 formed on
the AlN submount 18, a lead 19 made of a copper alloy having a
stepped part 19A on which the AlN submount 18 is mounted, an Au
stud bump 5 for electrically connecting the GaN-based LED element 2
to the circuit pattern 4, and a P.sub.2O.sub.5--F-based glass
sealing part 6 for surrounding and integrally sealing the GaN-based
LED element 2 and the lead 19.
The AlN submount 18 has a metallized circuit pattern.
The P.sub.2O.sub.5--F-based glass sealing part 6 is made of
P.sub.2O.sub.5--F-based low melting glass (coefficient of thermal
expansion: 16.9.times.10.sup.-6/.degree. C., yield point:
363.degree. C., refractive index: 1.54, internal transmittance: 99%
(470 nm)), and an optical shape face 6D, which is formed in a
semispherical form and functions to radiate light to a desired
radiation range, is formed based on hot pressing.
Two P.sub.2O.sub.5--F-based low melting glass sheets are set
parallel to each other so as to sandwich a lead 19, formed in the
lead frame, therebetween, and the assembly is hot pressed in a
nitrogen atmosphere under conditions of pressure 10 kgf and
temperature 410.degree. C. or above. Under the above conditions,
the viscosity of the low melting glass is 10.sup.8 to 10.sup.9
poises.
FIG. 23 is a diagram illustrating the state of glass sealing of the
lead frame by hot pressing. In this drawing, a lead frame 31 is
shown in which a pair of leads 311 made of a copper alloy sheet are
led out in a single direction. This lead frame 31 includes a lead
311 for fixing an AlN submount 18, an opening 312 provided on the
support side of the lead 311, an oval hole 313 for absorbing
thermal deformation of the lead frame 31, and a positioning hole
314 for positioning the feed position of the lead frame 31. The
periphery of the lead 311 is removed as an opening 310 in punching
out the copper alloy sheet.
The method for manufacturing the luminescent device 1 will be
explained.
A lead frame 31 with a lead 19 having a stepped part 19A for
mounting the AlN submount 18 is first formed. An AlN submount 18
with a circuit pattern 4 formed thereon is then bonded to the lead
frame 31. Next, a GaN-based LED element 2 is bonded by flip chip
binding through an Au stud bump 5 to the circuit pattern 4 provided
on the surface of the AlN submount 18. Next,
P.sub.2O.sub.5--F-based low melting glass is set parallel to each
other on and under the lead frame 31. The P.sub.2O.sub.5--F-based
low melting glass is then hot pressed using a mold (not shown). The
P.sub.2O.sub.5--F-based low melting glass is molded individually in
the small thickness part 6B and the P.sub.2O.sub.5--F-based glass
sealing part 6 based on hot pressing. Next, the lead 311 is cut for
isolation of luminescent devices from the lead frame 31.
The following effects can be attained by the ninth embodiment. (1)
Hot pressing is carried out using the P.sub.2O.sub.5--F-based low
melting glass in a highly viscose state. Therefore, glass sealing
at a temperature below the crystal growth temperature is possible.
(2) Since hot pressing is carried out in a nitrogen atmosphere,
each member is less likely to be oxidized. (3) Since two glass
sheets are set so as to sandwich a lead therebetween, sealing can
be carried out in a highly viscose state. (4) Since the
P.sub.2O.sub.5--F-based low melting glass and the copper alloy lead
are substantially equal to each other in coefficient of thermal
expansion, bonding failures such as separation and cracking are
less likely to occur. Further, even though there is a small
difference in coefficient of thermal expansion, the internal stress
can be absorbed based on the plasticity of copper as a soft metal.
In the first to eighth embodiments, a ceramic substrate with a
circuit pattern formed thereon was used as electric power supplying
means. The coefficient of thermal expansion of generally available
ceramic substrates is somewhat lower than that of the low melting
glass. Although the correlation is not necessarily great, there is
a tendency that materials having a weak intermolecular bond have a
lower melting point and, at the same time, have a higher
coefficient of thermal expansion. On the other hand, when a metal
lead is used as the electric power supplying means, even a lower
melting point glass with a coefficient of thermal expansion of not
less than 15.times.10.sup.-6/.degree. C. can realize a luminescent
device 1. When a material having a high coefficient of thermal
expansion is selected as the low melting glass, the difference in
coefficient of thermal expansion between the glass and the
GaN-based LED element becomes large. Therefore, in this case,
preferably, the measure for this difference is also carried out.
(5) Since flip chip mounting is adopted, damage to the electrode
part is less likely to occur. (6) In the structure, cracking
derived from the difference in coefficient of thermal expansion
between members is less likely to occur. Specifically, a stepped
part having a shape corresponding to the AlN submount is formed in
the lead, and, in the direction of the length of the AlN submount,
the stress can be relaxed by the plasticity of the soft metal lead.
Further, glass is likely to cause cracking upon exposure to tensile
stress and is less likely to cause cracking upon exposure to
compressive stress. A GaN-based LED element having a lower
coefficient of thermal expansion is located at the center part, and
the periphery thereof is surrounded by the lead having a higher
coefficient of thermal expansion and the P.sub.2O.sub.5--F-based
low melting glass. Therefore, the stress is vertically applied to
each face of the GaN-based LED element, and compressive stress
occurs in the glass. Thus, even when the coefficient of thermal
expansion of the low melting glass is larger than that of the LED
element and the submount, glass sealing can be realized. (7) Heat
generated from the GaN-based LED element is rapidly radiated to the
outside of the device through the AlN submount and the lead.
Further, since the coefficient of thermal expansion of the glass is
superior to the resin sealing material by a factor of about 10,
heat dissipation from the glass is not negligible. (8) A large
quantity of luminescent devices can be manufactured at a time by
conducting hot pressing to the lead frame for individual glass
sealing of leads and conducting tie bar cutting from the lead
frame, and, thus, excellent mass productivity can be realized.
The material for constituting the submount is not limited to AlN
and may be sapphire (Al.sub.2O.sub.3). When Al.sub.2O.sub.3 is
used, the difference in coefficient of thermal expansion between
Al.sub.2O.sub.3 and the glass material is small and, thus, the
occurrence of cracking and separation can be suppressed.
Further, as shown in FIG. 24, a construction may be adopted in
which a GaN-based LED element 2 is loaded on a Si submount 18 which
functions as a Zener diode by an n layer 18B and a p layer 18C. In
this case, the GaN-based LED element can be protected against
electrostatic discharge damage. For the wire 10 for electrically
connecting the p layer 18C in the Si submount 18 to the lead 19,
damage caused by glass sealing can be avoided by protection with a
protecting member such as the above-described heat resistant
inorganic material coating 11.
For the two glass sheets for sandwiching the lead therebetween,
white glass may be used on the lower side. In this case, light
emitted to the lower side can be reflected and radiated to the
optical shape formation side.
The two glass sheets for sandwiching the lead therebetween may be
different from each other in viscosity. Specifically,
P.sub.2O.sub.5--F-based low melting glass (coefficient of thermal
expansion: 17.3.times.10.sup.-6/.degree. C., yield point:
310.degree. C., refractive index: 1.51, internal transmittance: 99%
(470 nm)) is used as the upper glass, and P.sub.2O.sub.5--F-based
low melting glass (coefficient of thermal expansion:
16.9.times.10.sup.-6/.degree. C., yield point: 363.degree. C.,
refractive index: 1.54, internal transmittance: 99% (470 nm)) is
used as the lower glass. In this case, at the time of hot pressing,
the upper side is higher viscosity, and the lower side is lower
viscosity. This facilitates molding.
FIG. 25 is a luminescent device in the tenth embodiment, wherein
(a) is a plan view, (b) a cross-sectional view taken on line A-A of
(a), and (c) a perspective view of the lower glass. This
luminescent device 1 includes a face up-type GaN-based LED element
2, a lead 19 having a lead cup part 19B on which the GaN-based LED
element 2 is mounted, a wire 10 for electrically connecting the
GaN-based LED element 2 to the lead 19, a silicone coating 35 for
covering and protecting the GaN-based LED element 2 and the wire
10, and a P.sub.2O.sub.5--F-based glass sealing part 6 for
integrally sealing the lead 19 through the preformed upper glass
60A and lower glass 60B.
The lead cup part 19B is provided in a cone form by an inclined
face 190 and a bottom face 191 and is received in a lead receiving
groove 60C of the lower glass 60B shown in (c). The lead receiving
groove 60C is formed in preforming the lower glass 60B using a
mold.
The method for manufacturing the luminescent device 1 will be
explained.
At the outset, a lead frame (not shown) of copper provided with a
pair of leads 19 having a silver plated surface is provided. Next,
a GaN-based LED element 2 is mounted on the lead 19 in its lead cup
part 19B. The GaN-based LED element 2 is bonded to the lead cup
face 19B on its bottom face 191. The pair of leads 19 are then
electrically connected to the GaN-based LED element 2 on its
electrode through a wire 10. In such a state that the pair of leads
19 has been electrically connected to the GaN-based LED element 2,
the assembly is received in the lead receiving groove 60C in the
preformed lower glass 60B. A silicone resin coating 35 is then
potted so as to cover the pair of leads 19 and the GaN-based LED
element 2. The upper glass 60A is then provided and is integrated
with the lower glass 60B based on hot pressing. The luminescent
device 1 is cut out from the lead frame.
The following effects can be attained by the tenth embodiment.
In the silicone resin, the molecular bond is cleaved by heat at
about 400.degree. C. or above, and, consequently, gas is evolved.
Since the silicone resin coating 35 can be processed at 360.degree.
C. without heat decomposition, heat applied during the glass
sealing can be absorbed in the silicone resin to relax the stress.
Further, the use of the preformed lower glass 60B for receiving the
lead cup part 19B can stabilize glass sealing state of the pair of
leads 19. A large quantity of luminescent devices can be
manufactured at a time by conducting hot pressing to the lead frame
for individual glass sealing of leads and conducting tie bar
cutting from the lead frame, and, thus, excellent mass productivity
can be realized.
FIG. 26 is a cross-sectional view showing a first variant of the
luminescent device in the tenth embodiment. This luminescent device
1 is different from the device in the tenth embodiment in that the
luminescent device 1 includes a flip chip-type GaN-based LED
element 2 (0.3 mm.times.0.3 mm), an AlN submount 18 on which the
GaN-based LED element 2 is mounted, and a pair of lead frames 19
having a stepped part 19A for receiving the AlN submount 18.
The pair of lead frames 19 has an inclined face 19D above the
stepped part 19A, and light emitted from the GaN-based LED element
2 is reflected from the inclined face 19D for external
radiation.
The AlN submount 18 has via holes 18A for electrically connecting
the circuit pattern 4 provided on the surface to the circuit
pattern 4 provided on the backside.
The method for manufacturing the luminescent device 1 will be
explained.
A lead frame (not shown) provided with a pair of leads 19 is first
provided. Next, an AlN submount 18 is electrically connected
through an Ag paste so as to be located in a stepped part 19A in
the lead 19. A GaN-based LED element 2 is then bonded to the AlN
submount 18 through an Au stud bump 5. In such a state that the
pair of leads 19 are electrically connected to the GaN-based LED
element 2, the assembly is then received in the lead receiving
groove 60C of the preformed lower glass 60B. Next, a silicone
coating 35 is potted so as to cover the pair of leads 19 and the
GaN-based LED element 2. An upper glass 60A is then provided and is
integrated with a lower glass 60B by hot pressing. The luminescent
device 1 is then cut out from the lead frame.
In the first variant, light can be efficiently taken out from the
substrate side by using the flip chip-type GaN-based LED element
2.
FIG. 27 is a cross-sectional view of a second variant of the
luminescent device in the tenth embodiment. This luminescent device
1 is different from the device in the tenth embodiment in that the
luminescent device 1 includes a flip chip-type GaN-based LED
element (large size) 2, an AlN submount 18 on which the GaN-based
LED element 2 is mounted, and a pair of lead frames 19 having a
stepped part 19A for receiving the AlN submount 18. The size of the
large-size GaN-based LED element 2 is 1 mm.times.1 mm.
In the second variant, the construction using a large-size chip has
been explained. Since the chip size is large, the difference in
coefficient of thermal expansion between the
P.sub.2O.sub.5--F-based glass AlN submount 18 and the
P.sub.2O.sub.5--F-based glass sealing part 6 is large. Even in this
case, good sealing properties are obtained.
FIG. 28 shows a luminescent device in the eleventh embodiment,
wherein (a) is a side view and (b) a perspective view illustrating
glass sealing. As shown in FIG. 28 (a), in this luminescent device
1, a tubular body 60D made of P.sub.2O.sub.5--F-based glass is
heated to glass-seal the GaN-based LED element 2, the wire 10, and
the pair of leads 19.
As shown in FIG. 28 (b), the tubular body 60D is formed of a
partially cut-out tubular glass. The tubular body 60D is heated by
a heating device such as a burner (not shown) to melt the glass for
glass sealing of the GaN-based LED element 2, the wire 10, and the
pair of leads 19.
In the eleventh embodiment, the GaN-based LED element 2, the wire
10, and the pair of leads 19 can be glass-sealed based on the
surface tension of the melted glass. In this embodiment, glass
sealing is carried out by depositing the melted glass.
Alternatively, hot pressing may be carried out in such a state that
the glass is in a melted state.
FIG. 29 is a longitudinal sectional view of a luminescent device in
the twelfth embodiment. This luminescent device 1 is different from
the luminescent device 1 in the ninth embodiment in that a mold
part 9 made of an epoxy resin is provided.
The mold part 9 has a semispherical optical shape face 9A and is
formed by transfer molding.
According to this construction, an optical system can easily be
formed in the glass sealing-type device, and, at the same time, the
moisture resistance is further improved by surrounding the glass
sealing part 6 by the mold part 9. The lead-out part is not
directly from the glass, and, thus, cracking or breaking of glass
caused by stress or the like at the time of bending of the lead can
be advantageously prevented. The mold part 9 may be made of other
resin material other than the epoxy resin, for example, a silicone
resin, and molding methods other than transfer molding, for
example, potting molding, can also be applied. Alternatively, the
mold part 9 may be formed by an injection method using a resin
material such as acrylic or polycarbonate resin, and, in this case,
the productivity can be improved.
Embodiments shown in FIGS. 30 to 55 will be explained in
detail.
(Optical Element)
Optical elements include light emitting diodes, laser diodes, and
other light emitting elements and photodetectors. The wavelength of
light to be received and the wavelength of light to be emitted in
the optical element are not particularly limited, and, for example,
group III nitride-based compound semiconductor elements useful for
lights ranging from ultraviolet light to green light, and
GaAs-based semiconductor elements useful for red lights may be
used.
Group III nitride-based compound semiconductor light emitting
elements which emit short wavelengths pose a significant problem
associated with the sealing member. Group III nitride-based
compound semiconductors are represented by general formula
Al.sub.XGa.sub.YIn.sub.1-X-YN where 0<X.ltoreq.1,
0.ltoreq.Y.ltoreq.1, and 0.ltoreq.X+Y.ltoreq.1. Among them,
Al-containing group III nitride-based compound semiconductors
include the so-called binary systems of AlN, and the so-called
ternary systems of Al.sub.xGa.sub.1-xN and Al.sub.xIn.sub.1-xN
where 0<x<1. In the group III nitride-based compound
semiconductors and GaN, at least a part of the group III elements
may be replaced with boron (B), thallium (Tl) or the like. At least
a part of nitrogen (N) may also be replaced with phosphorus (P),
arsenic (As), antimony (Sb), bismuth (Bi) or the like.
The group III nitride-based compound semiconductor may contain any
dopant. n-type impurities usable herein include silicon (Si),
germanium (Ge), selenium (Se), tellurium (Te), and carbon (C).
p-type impurities usable herein include magnesium (Mg), zinc (Zn),
beryllium (Be), calcium (Ca), strontium (Sr), and barium (Ba).
After doping with the p-type impurity, the group III nitride-based
compound semiconductor may be exposed to electron beams, plasma, or
heat in an oven. This, however, is not indispensable.
The group III nitride-based compound semiconductor layer is formed
by an MOCVD (metal-organic vapor phase epitaxy) method. All the
semiconductor layers constituting the element are not always
required to be formed by the MOCVD method, and the MOCVD method may
be used in combination with a molecular beam epitaxy method (MBE
method), a halide vapor-phase epitaxy method (HVPE method),
sputtering, ion plating or the like.
Regarding the construction of the light emitting element, a homo
structure, hetero structure, or double hetero structure with MIS
junction, PIN junction or pn junction may be adopted. In the light
emitting layer, a quantum well structure (a single quantum well
structure or a multiple quantum well structure) may also be
adopted. The group III nitride-based compound semiconductor light
emitting element may be of a face-up type in which the main light
receiving/emitting direction (electrode face) is an optical axis
direction in the optical device, and a flip-chip type in which the
main light receiving/emitting direction is a direction opposite to
the optical axis direction and reflected light is utilized.
The heat resistant temperature of the group III nitride-based
compound semiconductor element is about 600.degree. C., and the
heat resistant temperature of the GaAs-based semiconductor element
is about 600.degree. C., and both the semiconductor elements are
stable against the temperature at which the low melting glass is
molded.
(Electric Power Receiving and Supplying Means)
The optical device includes electric power receiving and supplying
means. The electric power receiving and supplying means is an
electric component that functions to supply electric power to the
light emitting element and to take out electric power produced in a
photodetector upon exposure to light. The electric power receiving
and supplying means includes a lead for connecting the optical
device to electric wiring and a bonding wire for wiring the lead
and the optical element. The bonding wire is in many cases made of
a gold wire or a gold alloy wire. The heat resistant temperature of
the bonding wire per se and bonding between the bonding wire and
the lead or the optical element is 600.degree. C. or above, and
both the bonding wire per se and the bonding are stable against the
temperature at which the low melting glass is molded.
(First Sealing Member)
The first sealing member covers the optical element and at least a
part of the electric power receiving and supplying means. In this
invention, SiO.sub.2--Nb.sub.2O.sub.5-based,
B.sub.2O.sub.3--F-based, P.sub.2O.sub.5--F-based,
P.sub.2O.sub.5--ZnO-based,
SiO.sub.2--B.sub.2O.sub.3--La.sub.2O.sub.3-based or
SiO.sub.2--B.sub.2O.sub.3-based glass is selected as the first
sealing member.
All of these types of low melting glass can be pressed at 350 to
600.degree. C. The first sealing member in this invention can also
be formed by spontaneous welding.
A phosphor material can also be dispersed in the first sealing
material. An inorganic phosphor material powder may be used as the
phosphor material and may be mixed in the low melting glass.
Further, the low melting glass may also be doped with a rare earth
ion to render the glass fluorescent. Any desired luminescent color
including white light can be provided by properly combining a light
emitting element with a phosphor material.
In the combination of the first sealing member with the optical
element, preferably, the first sealing member has an Abbe number of
40 or less and a refractive index of 1.6 or more, and the optical
element has a receiving/emission wavelength of not more than 546.1
nm (wavelength of e-radiation of Na). Specifically, for the
external quantum efficiency of light emitted within the high
refractive index material, a higher refractive index of the sealing
material relative to the wavelength of light to be emitted is more
advantageous. The refractive index of the optical material is
defined by d-radiation of Na. In general, however, the refractive
index increased with decreasing the wavelength, and the level of a
change in refractive index with the wavelength of light is
expressed by the Abbe number. In particular, in a short-wavelength
emission-type light emitting element which poses a problem in
conventional resin sealing, the selection of a material which is
highly refractive in d-radiation of Na and undergoes a large change
in refractive index with wavelength, can prevent a lowering in
light output caused by yellowing of the resin and, in addition, can
realize sealing with a material having a high refractive index for
short wavelength light, and thus, high external quantum efficiency
can be provided.
SiO.sub.2--Nb.sub.2O.sub.5-based glass may be mentioned as low
melting glass having such optical characteristics. Among others,
SiO.sub.2--Nb.sub.2O.sub.5--Na.sub.2O glass is preferred.
Preferably, in the light emitting element, the first sealing member
is disposed in at least a light receiving/emission direction to
cover the light emitting element for reliably preventing
discoloration in this direction.
The first sealing member may be in any form without particular
limitation and properly designed according to optical
characteristics required of the optical device. In the case of a
light emitting element, the first sealing member disposed in the
light release direction is preferably in a convex-lens form.
(Second Sealing Member)
In this invention, the optical element is sometimes sealed with a
plurality of sealing members including the above first sealing
member. Here the second sealing member covers the optical element
from a part opposite to the main light receiving/emission
direction.
As with the first sealing member, the second sealing member may
also be made of low melting glass selected from
SiO.sub.2--Nb.sub.2O.sub.5-based, B.sub.2O.sub.3--F-based,
P.sub.2O.sub.5--F-based, P.sub.2O.sub.5--ZnO-based,
SiO.sub.2--B.sub.2O.sub.3--La.sub.2O.sub.3-based or
SiO.sub.2--B.sub.2O.sub.3-based glass. The second sealing member
and the first sealing member may be the same or different.
When the members are different low melting glass materials,
preferably, the refractive index of the first sealing member
(provided in the main light receiving/emission direction of the
optical element) is higher than the refractive index of the second
sealing member. According to this construction, when a light
emitting element is used as the optical element, the critical angle
at the interface of the light emitting element and the sealing
member is increased to improve the light efficiency.
As with the first sealing member, the second sealing member made of
low melting glass can be formed by press molding or spontaneous
welding.
As with the first sealing member, a phosphor material may also be
dispersed in the second sealing member made of low melting
glass.
The second sealing member may be made of a nontransparent material.
In addition to low melting glass, for example, metal plates and
ceramic plates may be mentioned as the second sealing member. In
this case, preferably, the second sealing member is made of a
material which can efficiently reflect light. When the second
sealing member is made of a material other than the low melting
glass, preferably, the coefficient of linear expansion of the first
sealing member is between the coefficient of linear expansion of
the second sealing member and the coefficient of linear expansion
of the optical element. According to this construction, even when
the optical device is heat treated in a solder reflow oven or the
like, the internal stress of the optical device based on the
difference in coefficient of linear expansion between dissimilar
materials can be reduced.
This invention will be explained with reference to the following
examples.
EXAMPLE 1
In this example, a face-up-type group III nitride-based compound
semiconductor light emitting element 1010 shown in FIG. 30 was used
as an optical element. This light emitting element emits blue
light.
The specifications of each layer constituting the light emitting
element 1010 are as follows.
TABLE-US-00001 Layers Composition p-type layer 1015 p-GaN:Mg Layer
1014 including light Including InGaN layer emitting layer n-type
layer 1013 n-GaN:Si Buffer layer 1012 AlN Substrate 1011
Sapphire
The n-type layer 1013 made of GaN doped with Si as an n-type
impurity is formed on the substrate 1011 through the buffer layer
1012. In this example, sapphire is used as the substrate 1011. The
material for the substrate 1011, however, is not limited to
sapphire, and examples of materials usable herein include sapphire,
spinel, silicon carbide, zinc oxide, magnesium oxide, manganese
oxide, zirconium boride, and group III nitride-based compound
semiconductor single crystals. The buffer layer is formed by MOCVD
using AlN. The material for the buffer layer, however, is not
limited to AlN, and other materials such as GaN, InN, AlGaN, InGaN
and AlInGaN may also be used. For example, a molecular beam epitaxy
method (MBE method), a halide vapor-phase epitaxy method (HVPE
method), sputtering, or ion plating may be used for the formation
of the buffer layer. When the substrate is made of a group III
nitride-based compound semiconductor, the provision of the buffer
layer can be omitted.
The substrate and the buffer layer can be if necessary removed
after semiconductor element formation.
In this example, the n-type layer 1013 is made of GaN.
Alternatively, the n-type layer 1013 may be made of AlGaN, InGaN or
AlInGaN.
Further, the n-type layer 1013 has been doped with Si as an n-type
impurity. Other n-type impurities usable herein include Ge, Se, Te,
and C.
The layer 1014 including a light emitting layer may comprise a
quantum well structure (a multiple quantum well structure or a
single quantum well structure), and the structure of the light
emitting element may be of single hetero type, double hetero type,
and homojunction type.
The layer 1014 including a light emitting layer may also include,
on its p-type layer 1015 side, a group III nitride-based compound
semiconductor layer with a broad bandgap doped with Mg or the like.
This can effectively prevent electrons injected into the layer 1014
including a light emitting layer from diffusing into the p-type
layer 1015.
The p-type layer 1015 made of GaN doped with Mg as a p-type
impurity is formed on the layer 1014 including a light emitting
layer. The p-type layer 1015 may also be made of AlGaN, InGaN or
InAlGaN. Zn, Be, Ca, Sr, or Ba may also be used as the p-type
impurity. After the introduction of the p-type impurity, the
resistance can be lowered by a well-known method such as electron
beam irradiation, heating in an oven, or plasma irradiation. In the
light emitting element having the above construction, each group
III nitride-based compound semiconductor layer may be formed by
MOCVD under conventional conditions, or alternatively may be formed
by a method such as a molecular beam epitaxy method (MBE method), a
halide vapor-phase epitaxy method (HVPE method), sputtering, or ion
plating.
An n-electrode 1018 has a two-layer structure of an Al layer and a
V layer. After the formation of the p-type layer 1015, the p-type
layer 1015, the layer 1014 including a light emitting layer, and a
part of the n-type layer 1013 are removed by etching to expose the
n-type layer 1013, and the n-electrode 1018 is formed by vapor
deposition on the exposed n-type layer 1013.
A light transparent electrode 1016, which is a gold-containing thin
film, is stacked on the p-type layer 1015. A p-electrode 1017 is
also made of a gold-containing material and is formed by vapor
deposition on the light transparent electrode 1016. After the
formation of the individual layers and electrodes by the above
steps, the step of isolating chips is carried out.
As shown in FIG. 31, in the light emitting element 1010, a light
emitting element 1010 is fixed onto a mount lead 1021 as electric
power receiving and supplying means, and bonding wires 1023, 1024
are suspended from the upper electrodes in the light emitting
element 1010 respectively to a mount lead 1021 and a sublead 1022
as other electric power receiving and supplying means. The surface
of the mount lead 1021 is plated with silver from the viewpoint of
efficiently reflecting light from the light emitting element 1010.
In order to ensure light reflection efficiency, the light emitting
element 1010 can also be fixed onto the mount lead 1021 with the
aid of an inorganic white adhesive. Further, a high level of heat
dissipation can be imparted by using a copper alloy close to pure
copper. A gold wire is used as the bonding wire.
An assembly 1020 shown in FIG. 30 is set as a core in a pressing
mold 1025 as shown in FIG. 32. Low melting glass is previously set
in each of concave parts 1026, 1027 in the pressing mold 1025, and
the mold 1025 is then closed to mold a sealing member 1028 (first
sealing member) shown in FIG. 33. In this example,
P.sub.2O.sub.5--F-based glass (Sumita Optical Glass, Inc.: trade
name K-PG325) was selected as the low melting glass, and the
molding temperature was brought to 430.degree. C.
As a result, as shown in FIG. 33, the whole light emitting element
1010 and a part of the lead parts 1021, 1022 are covered by a
hemispherical sealing member 1028. The shape of the sealing member
1028 can be properly designed according to optical properties
required of the optical device 1002, and, for example, the sealing
member 1028 may have a shell shape.
EXAMPLE 2
An optical device 1003 shown in FIG. 34 has the same construction
as the optical device 1001 shown in FIG. 33, except that the low
melting glass contains a fluorescent material. In FIGS. 33 and 34,
like parts are identified with the same reference numerals, and the
explanation thereof will be omitted. In this example, the sealing
member 1038 is made of low melting glass doped with a rare earth
element as the fluorescent material.
The incorporation of an optional fluorescent material in the low
melting glass can realize control of the color of light emitted
from the optical device 1003.
EXAMPLE 3
An optical device 1004 shown in FIG. 35 has the same construction
as the optical device 1002 shown in FIG. 4, except that the sealing
member 1028 is covered by a shell-shaped cover 1048. This cover
1048 is made of an epoxy resin or other light transparent resin and
is formed by molding. The provision of the cover 1048 can provide a
large optical device. Thus, a wide variety of optical systems can
be provided by preparing a glass sealing body having a standard
shape and then using a resin for which equipment of mold and
molding work are easier. In this case, the density of light emitted
from the light emitting element is high, and a glass material is
provided around the light emitting element which causes a
temperature rise. Therefore, deterioration in the optical output
can be suppressed to such a level that is negligible. The sealing
member 1038 shown in FIG. 34 can also be covered by this cover
1048. Further, each of sealing members 1058, 1068, 1069, 1079 shown
in FIGS. 36, 38, and 39 which will be described later can also be
covered by this cover 1048. This cover 1048 can contain a
fluorescent material.
EXAMPLE 4
An optical device 1005 shown in FIG. 36 includes a sealing member
1058 formed by spontaneous adhesion. In FIGS. 33 and 36, like parts
are identified with the same reference characters, and the
explanation thereof will be omitted.
The sealing member 1058 is formed as follows. As shown in FIG. 37,
a cylindrical body 1058a made of low melting glass is provided and
put on an assembly 1020 of a light emitting element 1010 and lead
parts 1021, 1022. This is placed in an oven to soften the
cylindrical body 1058a. As a result, the cylindrical body 1058a
covers, in a lens form by the surface tension of the material, the
assembly 1020.
According to this example, the need to use the pressing mold can be
eliminated, and, thus, optical devices can be provided at low
cost.
EXAMPLE 5
An optical device 1006 shown in FIG. 38 has the same construction
as the optical device shown in FIG. 33, except that the light
emitting element 1010 and the lead parts 1021, 1022 are covered by
dissimilar types of low melting glass. In FIGS. 33 and 38, like
parts are identified with the same reference characters, and the
explanation thereof will be omitted.
In the optical device shown in FIG. 38, as with the optical device
described above, a blue light emitting element is used as the light
emitting element. However, the upper side (a main light emission
direction) of the light emitting element 1010 is sealed with a
first sealing member 6108 made of SiO.sub.2--Nb.sub.2O.sub.5-based
glass (refractive index 1.8, Abbe number 25), and the lower side (a
direction opposite to the main light emission direction) of the
light emitting element 1010 is sealed with a second sealing member
1069 made of P.sub.2O.sub.5--F-based glass. From the viewpoint of
improving light takeout efficiency, a material having a high
refractive index is selected as the material for the first sealing
member 1068. Further, the restriction on the manufacture caused by
this is relaxed by the second sealing member, and this construction
can be actually prepared. As a result, the refractive index of the
first sealing member 1068 is higher than that of the second sealing
member 1069. A material having a small Abbe number is selected as
the material for the first sealing member 1068 so that the actual
refractive index of the first sealing member 1068 is larger than
the blue light emitting element.
The optical device 1006 shown in FIG. 38 can be formed by using the
mold 1025 shown in FIG. 32. In this case, the material filled into
the concave part 1026 is different from the material filled into
the concave part 1027.
When a red light emitting element is used, a material having a high
refractive index and a large Abbe number is selected as the
material for the first sealing member 1068, whereby a high
refractive index can be actually selected. An example of this
material is SiO.sub.2--B.sub.2O.sub.3--La.sub.2O.sub.3-based glass
having a refractive index of 1.8 and an Abbe number of 45.
EXAMPLE 6
An optical device 1007 shown in FIG. 39 has the same construction
as the optical device shown in FIG. 38, except that a metallic thin
sheet (Al thin sheet) was used as the second sealing member 1079.
In FIGS. 38 and 39, like parts are identified with the same
reference characters, and the explanation thereof will be omitted.
Light can be efficiently reflected from the light emitting element
1010 by using a metallic material as the second sealing member. The
second sealing member 1079 entirely functions as a reflector plate.
In addition to the metallic thin sheet, for example, a resin sheet
or the like may be used.
This optical device 1007 is manufactured as follows. As shown in
FIG. 40, the metallic thin sheet 1079 is applied to the backside of
an assembly 1020 of the light emitting element 1010 and the lead
parts 1021, 1022. This assembly 1020 is set as a core in the mold
1025. In this case, the low melting glass is filled into only the
upper concave part 1026 in the pressing mold 1025. Thereafter, the
mold is clamped to provide the optical device 1007 shown in FIG.
39.
As in this example, when the material for the first sealing member
1068 and the material for the second sealing member 1079 are
different from each other, preferably, the value of the coefficient
of linear expansion of the first sealing member is intermediate
between the coefficient of linear expansion of the second sealing
member and the coefficient of linear expansion of the light
emitting element.
EXAMPLE 7
In this example, a flip chip-type light emitting element 1100 is
used. As shown in FIG. 41, the flip chip-type light emitting
element has the same construction as the light emitting element
shown in FIG. 30, except that, in stead of the light transparent
electrode 1016 and the p-electrode 1017, a p-electrode 1101 as a
thick film is stacked on the whole area of the p-type layer 1015.
In FIGS. 30 and 41, like parts are identified with the same
reference characters, and the explanation thereof will be
omitted.
The flip chip-type light emitting element 1100 is mounted on a
mount lead 1021 through a submount 1110. The submount 1110 and the
sublead 1022 are wire connected through a bonding wire 1124 to form
an assembly 1120. A circuit pattern is formed in this submount
1110, and electrodes 1018, 1101 in the light emitting element 1100
are electrically connected to lead parts 1021, 1022 directly or
through a bonding wire 1124. In the same manner as in Example 1, a
sealing member 1028 is formed using this assembly 1120 as a core to
provide an optical device 1008 shown in FIG. 42. In a luminescent
device provided with the flip chip-type light emitting element, the
necessary number of bonding wires which are delicate in the sealing
step is only one. Therefore, the process control becomes easy, and,
further, the production yield is improved. Further, since the
bonding wire is not in proximity to the light emitting element in
its light emitting face, the bonding wire does not affect external
radiation efficiency.
The same elements as in Example 1 are identified with the same
reference characters for simplification of explanation.
The sealing members explained in Examples 2 to 6 can be applied to
the assembly 1120 of the flip chip-type light emitting element 1100
shown in FIG. 41. Embodiments thereof are shown in FIGS. 42 to 45.
For simplification of the explanation, the same elements as
described above are identified with the same reference characters,
and the explanation thereof will be omitted.
EXAMPLE 8
In this example, as shown in FIG. 47, circuit patterns 1201, 1202
as electric power receiving and supplying means are formed on the
surface of an inorganic material substrate 1200 made of AlN or the
like. A flip chip-type light emitting element 1100 is mounted on
the circuit patterns 1201, 1202 through bumps 1205, 1206. The
substrate 1200 is mounted on lead parts 1021, 1022 through a
eutectic material. In the same manner as in Example 1, a sealing
member 1028 is formed using this assembly 1220 as a core to provide
an optical device 1009 shown in FIG. 48.
The same elements as in Example 1 are identified with the same
reference characters for simplification of the explanation
thereof.
The sealing members explained in Examples 2 to 6 can be applied to
the assembly 1220 shown in FIG. 47. Embodiments thereof are shown
in FIGS. 49 to 51. In FIGS. 49 to 51, for simplification of the
explanation, the same elements as described above are identified
with the same reference characters, and the explanation thereof is
omitted.
In the above embodiments, the whole assembly 1220 is covered by a
sealing member. Alternatively, as shown in FIG. 52, the light
emitting element 1100 and a part of the circuit patterns 1201, 1202
may be covered by a sealing member 1228. The optical device shown
in FIG. 53 can be used as chip LED.
In the optical device in this example, the thermally or
mechanically weak bonding wire is absent, and any organic material
is not included in the device. Therefore, the low melting glass can
be press molded at a higher temperature. Further, stability against
heat treatment in a reflow oven or the like can be improved.
Accordingly, the device can be manufactured more easily, and the
range of choice of the applicable low melting glass can also be
broadened. Thus, the optical device can be provided at lower
cost.
Without limitation to the eutectic material, the optical element
can be mounted through a gold bump. Also in this case, a stable
wireless device consisting of inorganic materials only can be
formed.
EXAMPLE 9
An optical device in this example is shown in FIG. 54
(cross-sectional view) and FIG. 55 (plan view).
This optical device 1230 includes a flip chip-type light emitting
element 1100, an AlN substrate 1231, a metal pattern 1236, and a
sealing member 1238.
In this example, the substrate 1231 is made of AlN. However, any
material can be used so far as at least the mounting face of the
light emitting element 1100 is made of an insulating material such
as AlN. For example, the substrate may be such that the base part
of the substrate is made of an aluminum plate and AlN is stacked
onto the surface of the aluminum plate. In addition to AlN, for
example, Al.sub.2O.sub.3 may be used as the insulating
material.
Through-holes 1231, 1232 are provided in the substrate 1231.
Substantially the whole area of the mounting face of the substrate
1231 is covered by metal patterns 1235, 1236. In this example, the
metal patterns 1235, 1236 are formed by a metallization method.
Therefore, the bonding force between the metal patterns 1235, 1236
and the substrate 1231 is high, and increasing the area of contact
between the substrate 1231 and the metal patterns 1235, 1236 can
further improve the bonding strength between the substrate and the
metal patterns. In this example, the metal patterns 1235, 1236
comprise tungsten plated with nickel, and, in the light emitting
element mount part and the metal pattern exposed part (part not
sealed with low melting glass), gold plating is further provided.
The metal material has a high level of strength of bonding to the
insulating material on the substrate mount face and the sealing
member of low melting glass. Further, since the glass and the metal
material are substantially identical to each other in coefficient
of linear thermal expansion (approximately 10 to 20.times.10.sup.-6
(1/.degree. C.)), the thermal shrinkage-derived stress is less
likely to occur. The form of the metal pattern and the forming
material may be properly selected depending upon the material of
the substrate mount face and the material of the sealing
member.
The metal patterns 1235, 1236 function as electric power receiving
and supplying means for the light emitting element 1100.
Alternatively, separately from the electric power receiving and
supplying means, the metal pattern may be formed to ensure bonding
strength between the substrate and the sealing member.
The flip chip-type light emitting element 1100 on its electrode
face (lower side face in the drawing) is plated with a eutectic
material. This is passed into a general-purpose reflow oven to
solder the light emitting element 1100 to the metal patterns 1235,
1236.
Here since the eutectic material plating is widely and thinly
applied on the surface of the electrode in the light emitting
element 1100, heat dissipation to the substrate side is excellent.
Further, even when the spacing between the p-electrode and the
n-electrode is small as in the flip chip-type light emitting
element, there is no fear of short-circuiting.
The sealing member 1238 is made of low melting glass transparent to
wavelength in the light emitting element 1100. Low melting glass
selected from SiO.sub.2--Nb.sub.2O.sub.5-based,
B.sub.2O.sub.3--F-based, P.sub.2O.sub.5--F-based,
P.sub.2O.sub.5--ZnO-based,
SiO.sub.2--B.sub.2O.sub.3--La.sub.2O.sub.3-based and
SiO.sub.2--B.sub.2O.sub.3-based low melting glasses can be adopted
as the low melting glass.
The sealing member 1238 may be molded under the reduced pressure in
a nitrogen atmosphere.
According to the optical device 1230, the adhesion between the low
melting glass constituting the sealing member 1238 and the metal
constituting the metal patterns 1235, 1236 is high, and, further, a
high level of adhesion between the above metal and the AlN
substrate 1231 is also ensured. Therefore, the sealing member 1238
is strongly bonded to the substrate 1231, and interfacial peeling
hardly occurs. Further, in this optical device, the thermally or
mechanically brittle bonding wire is absent, and, in addition, no
organic material is contained in the device. Therefore, the low
melting glass can be pressed at higher temperatures. Further, the
device is stable against heat treatment in a reflow oven or the
like. Accordingly, the device can be manufactured more easily, and
the range of choice of the applicable low melting glass can also be
broadened.
Embodiments shown in FIGS. 56 to 64 will be explained in
detail.
(Optical Element)
Optical elements include light emitting diodes, laser diodes, and
other light emitting elements and photodetectors. The wavelength of
light to be received and the wavelength of light to be emitted in
the optical element are not particularly limited, and, for example,
group III nitride-based compound semiconductor elements useful for
lights ranging from ultraviolet light to green light, and
GaAs-based semiconductor elements useful for red lights may be
used. Other optical elements usable herein include those made of
SiC, AlInGaP and the like.
Group III nitride-based compound semiconductor light emitting
elements which emit short wavelengths pose a significant problem
associated with the sealing member. Group III nitride-based
compound semiconductors are represented by general formula
Al.sub.xGa.sub.yIn.sub.1-x-yN where 0<x.ltoreq.1,
0.ltoreq.y.ltoreq.1, and 0.ltoreq.x+y.ltoreq.1. Among them,
Al-containing group III nitride-based compound semiconductors
include the so-called binary systems of AlN, and the so-called
ternary systems of Al.sub.xGa.sub.1-xN and Al.sub.xIn.sub.1-xN
where 0<x<1. In the group III nitride-based compound
semiconductors and GaN, at least a part of the group III elements
may be replaced with boron (B), thallium (Tl) or the like. At least
a part of nitrogen (N) may also be replaced with phosphorus (P),
arsenic (As), antimony (Sb), bismuth (Bi) or the like.
The group III nitride-based compound semiconductor may contain any
dopant. n-type impurities usable herein include silicon (Si),
germanium (Ge), selenium (Se), tellurium (Te), and carbon (C).
p-type impurities usable herein include magnesium (Mg), zinc (Zn),
beryllium (Be), calcium (Ca), strontium (Sr), and barium (Ba).
After doping with the p-type impurity, the group III nitride-based
compound semiconductor may be exposed to electron beams, plasma, or
heat in an oven. This, however, is not indispensable.
The group III nitride-based compound semiconductor layer is formed
by an MOCVD (metal-organic vapor phase epitaxy) method. All the
semiconductor layers constituting the element are not always
required to be formed by the MOCVD method, and the MOCVD method may
be used in combination with a molecular beam epitaxy method (MBE
method), a halide vapor-phase epitaxy method (HVPE method),
sputtering, ion plating or the like.
Regarding the construction of the light emitting element, a homo
structure, hetero structure, or double hetero structure with MIS
junction, PIN junction or pn junction may be adopted. In the light
emitting layer, a quantum well structure (a single quantum well
structure or a multiple quantum well structure) may also be
adopted. The group III nitride-based compound semiconductor light
emitting element may be of a face-up type in which the main light
receiving/emitting direction (electrode face) is an optical axis
direction in the optical device, and a flip-chip type in which the
main light receiving/emitting direction is a direction opposite to
the optical axis direction and reflected light is utilized.
The epitaxial growth temperature of the group III nitride-based
compound semiconductor element is about 1050.degree. C., and,
regarding the epitaxial growth temperature of the GaAs-based
semiconductor element, the heat resistant temperature is
600.degree. C. or above. In both the cases, the use of low melting
glass can realize processing without heat damage.
(Inorganic Material Substrate)
In the optical device of this invention, the above-mentioned
optical element is mounted on an inorganic material substrate. The
base material and the form of the inorganic material substrate may
be properly selected depending upon applications of the optical
device. For example, rectangular plates of AlN, Al.sub.2O.sub.3,
glass-containing Al.sub.2O.sub.3 or the like may be used.
Any substrate may be used so far as at least the surface of the
substrate is made of the base material. For example, a substrate
may be used in which the center part is made of Al or Al alloy, and
the surface thereof is surrounded by AlN.
(Metal Pattern)
A metal pattern is formed on the inorganic material substrate and
functions to electrically connect each electrode in the optical
element to an external circuit for receiving electric power from
the optical element or supplying electric power to the optical
element. Specifically, when the optical element is a light emitting
element, electric power is applied from an external circuit to the
optical element, while when the optical element is a photodetector,
electric power generated in the optical element is output to an
external circuit.
In addition to electric power supplying/receiving function, the
metal pattern according to the invention functions also as an
adhesive layer for stable adhesion of the inorganic sealing member
to the inorganic material substrate. The sealing member is disposed
so as to surround the optical element. Therefore, when the metal
pattern is also formed in an area surrounding the optical element,
the area of the metal pattern interposed between the sealing member
and the inorganic material substrate can be maximized. The metal
pattern surrounding the optical element is not limited to a
continuous pattern and may be noncontinuous. The whole
noncontinuous metal pattern is not always required to bear the
electric power supplying/receiving function.
The metal pattern further functions to reflect light. Therefore,
when the metal pattern is provided so as to surround the optical
element, light emitted from the optical element can be wholly
reflected from the metal pattern, contributing to improved light
takeout efficiency. For example, a black substrate of AlN
disadvantageously absorbs light emitted from the optical element,
and a substrate of Al.sub.2O.sub.3 is disadvantageously transparent
to light emitted from the optical element. In this case, when the
optical element is surrounded by the metal pattern, the light
emitted from the optical element can be efficiently reflected from
the metal pattern and can be led to the outside of the device.
The material for metal pattern formation is properly selected
depending upon the material for the sealing member and the material
for the inorganic material substrate so that the material for metal
pattern formation is bonded with good boding strength to the
sealing member and the inorganic material substrate. The metal
pattern may have a multilayered structure. For example, W, W\Ni (Ni
being stacked on W), W\Ni\Ag (Ni and Ag being stacked in that order
on W), and copper foils may be adopted as the material for metal
pattern formation.
Upon heating, the W layer enters in a wedge form into the sealing
member and the inorganic material in the substrate to form strong
bonding between the sealing member and the inorganic material in
the substrate. When the Ni layer is formed on the W layer, upon
heating, a chemical bond is formed between the Ni layer and the
sealing member, whereby the Ni layer and the sealing member are
strongly boned to each other.
The Ag layer is a high-reflectance layer for improving the light
reflection efficiency of the metal pattern and is preferably
partially formed on a peripheral site of the optical element.
Further, an Au layer may be formed as bonding means on the optical
element mount part. The optical element can be bonded to the metal
pattern through the Au layer.
An Au bump may be used as bonding means. In addition to the Au
bump, mount bonding means using a eutectic material such as solder
bumps or solder plating may also be used.
From the reducing the heat distortion level of the substrate, the
metal pattern is preferably formed on substantially the whole area
of the optical element mount face (surface) of the substrate.
When the metal pattern is formed so as to extend to the backside of
the substrate, a through-hole (via hole) is formed in the
substrate, and the material for the metal pattern can be extended
through the hole to connect the pattern on the substrate surface to
the pattern on the backside of the substrate. An electric terminal
is drawn from the optical element mount face of the substrate to
the backside thereof. Therefore, there is no need particular to
provide a part, not covered by the sealing member of the optical
element for the electric terminal, on the optical element mount
face side of the substrate, and the whole area can be sealed with a
plate-shaped sealing member. Therefore, the mass productivity is
excellent. In this case, when any through-hole is not provided in
the substrate, the sealing member of the optical element on the
optical element mount face side does not reach the backside
thereof.
The method for metal pattern formation is not particularly limited.
In the working example, a paste of W was screen printed on an
inorganic material substrate, and the print was then fired to form
a metal pattern of W on the inorganic material substrate. This W
layer was plated with an Ni layer to form a metal pattern of W\Ni,
followed by heat treatment. In the case of W\Ni\Ag, the Ni layer
formed by plating is further plated with Ag.
Alternatively, these metal layers may be formed by sputtering or
other well known methods.
(Sealing Member)
The inorganic sealing member is not particularly limited so far as
it is transparent to the wavelength of received or emitted light in
the optical element and can protect the optical element. When the
fact that the heat resistant temperature of the optical element is
about 600.degree. C. is taken into consideration, however, the
adoption of low melting glass having a melting point (softening
point) below the heat resistant temperature is preferred.
In addition to lead glass and chalcogenide glass,
SiO.sub.2--Nb.sub.2O.sub.5-based, B.sub.2O.sub.3--F-based,
P.sub.2O.sub.5--F-based, P.sub.2O.sub.5--ZnO-based,
SiO.sub.2--B.sub.2O.sub.3--La2O.sub.3-based or
SiO.sub.2--B.sub.2O.sub.3-based glasses may be adopted as the low
melting glass. All of these low melting glasses can be pressed at
350 to 600.degree. C.
A fluorescent material can also be dispersed in the sealing member.
An inorganic fluorescent material powder can be used as the
fluorescent material and can be mixed into the low melting glass.
Further, rare earth ions can be doped into the low melting glass to
yield fluorescence. A proper combination of a light emitting
element with a fluorescent material can produce desired luminescent
colors including white light.
In the combination of the sealing member with the optical element,
preferably, the Abbe number of the sealing member is 40 or less,
the refractive index is 1.6 or more, and the wavelength of light
reception and light emission of the optical element is brought to
not more than 546.1 nm (wavelength of e radiation of Na).
Specifically, regarding the external quantum efficiency of light
emitted within the high refractive index material, a higher
refractive index of the sealing material with respect to the
wavelength of emitted light is more advantageous. The refractive
index of the optical material is defined by d radiation of Na. In
general, however, the refractive index increases with reducing the
wavelength, and the level of a change in refractive index as a
function of light wavelength is indicated by the Abbe number. In
particular, in the light emitting element of short wavelength
emission which poses a problem associated with the conventional
resin sealing, selecting a material which is high in refractive
index in d radiation of Na and causes a significant change in
refractive index with respect to the wavelength can prevent a
lowering in output of light caused by yellowing of the resin. In
addition, in essence, regarding short wavelength light, sealing
with a high refractive index material can be realized, and high
external quantum efficiency can be provided.
SiO.sub.2--Nb.sub.2O.sub.5-based glass may be mentioned as the low
melting glass having the above optical properties. Among others,
SiO.sub.2--Nb.sub.2O.sub.5--Na.sub.2O glass is preferred.
When a sealing member of a low melting glass sheet is put on an
optical element followed by heating for softening, the light
emitting element can be surrounded by the sealing member. This
heating is preferably carried out under a reduced pressure
atmosphere to prevent the entry of air into between the sealing
member and the optical element. Upon heating, a chemical reaction
takes place at the interface of the low melting glass and the metal
pattern, whereby both the materials are strongly bonded to each
other.
The following examples further illustrate this invention.
EXAMPLE 10
In this example, a flip chip-type group III nitride-based compound
semiconductor light emitting element 2010 shown in FIG. 56 was used
as an optical element. This light emitting element emits blue
light.
The specifications of each layer constituting the light emitting
element 2010 are as follows.
TABLE-US-00002 Layers Composition p-type layer 2015 p-GaN:Mg Layer
2014 including light Including InGaN layer emitting layer n-type
layer 2013 n-GaN:Si Buffer layer 2012 AlN Substrate 2011
Sapphire
The n-type layer 2013 made of GaN doped with Si as an n-type
impurity is formed on the substrate 2011 through the buffer layer
12. In this example, sapphire is used as the substrate 2011. The
material for the substrate 2011, however, is not limited to
sapphire, and examples of materials usable herein include sapphire,
spinel, silicon carbide, zinc oxide, magnesium oxide, manganese
oxide, zirconium boride, and group III nitride-based compound
semiconductor single crystals. The buffer layer is formed by MOCVD
using AlN. The material for the buffer layer, however, is not
limited to AlN, and other materials such as GaN, InN, AlGaN, InGaN
and AlInGaN may also be used. For example, a molecular beam epitaxy
method (MBE method), a halide vapor-phase epitaxy method (HVPE
method), sputtering, or ion plating may be used for the formation
of the buffer layer. When the substrate is made of a group III
nitride-based compound semiconductor, the provision of the buffer
layer can be omitted.
The substrate and the buffer layer can be if necessary removed
after semiconductor element formation.
In this example, the n-type layer 2013 is made of GaN.
Alternatively, the n-type layer 2013 may be made of AlGaN, InGaN or
AlInGaN.
Further, the n-type layer 2013 has been doped with Si as an n-type
impurity. Other n-type impurities usable herein include Ge, Se, Te,
and C.
The layer 2014 including a light emitting layer may comprise a
quantum well structure (a multiple quantum well structure or a
single quantum well structure), and the structure of the light
emitting element may be of single hetero type, double hetero type,
and homojunction type.
The layer 2014 including a light emitting layer may also include,
on its p-type layer 2015 side, a group III nitride-based compound
semiconductor layer with a broad bandgap doped with Mg or the like.
This can effectively prevent electrons injected into the layer 2014
including a light emitting layer from diffusing into the p-type
layer 2015.
The p-type layer 2015 made of GaN doped with Mg as a p-type
impurity is formed on the layer 2014 including a light emitting
layer. The p-type layer 2015 may also be made of AlGaN, InGaN or
InAlGaN. Zn, Be, Ca, Sr, or Ba may also be used as the p-type
impurity. After the introduction of the p-type impurity, the
resistance can be lowered by a well-known method such as electron
beam irradiation, heating in an oven, or plasma irradiation.
In the light emitting element having the above construction, each
group III nitride-based compound semiconductor layer may be formed
by MOCVD under conventional conditions, or alternatively may be
formed by a method such as a molecular beam epitaxy method (MBE
method), a halide vapor-phase epitaxy method (HVPE method),
sputtering, or ion plating.
An n-electrode 2018 has a two-layer structure of an Al layer and a
V layer. After the formation of the p-type layer 2015, the p-type
layer 2015, the layer 2014 including a light emitting layer, and a
part of the n-type layer 2013 are removed by etching to expose the
n-type layer 2013, and the n-electrode 2018 is then formed on the
exposed n-type layer 2013 by vapor deposition.
A p-electrode 2016 is stacked on the p-type layer 2015 by vapor
deposition. After the formation of the individual layers and
electrodes by the above steps, the step of isolating chips is
carried out.
Next, an inorganic material substrate for mounting this light
emitting element 2010 is provided.
A W-containing paste is screen printed on both sides of the
inorganic material substrate 2021 of AlN before firing to form
patterns 2023, 2024 shown in FIG. 57. As shown in FIG. 57 (b), a
through-hole 2025 is formed in the substrate 2021. A pattern 2023
of the mount face (surface) is electrically connected to a pattern
2024 on the backside through the through-hole 2025.
Thereafter, AlN is sintered at a temperature above 1500.degree. C.,
and the W paste is baked onto the substrate 2021, whereby W is
strongly bonded to the substrate. This W can also be formed by
sputtering. Alternatively, instead of W, a high melting metal such
as Mo may be used.
Next, the top of the W pattern 2023 on the surface side of the
substrate 2021 is plated with an Ni layer 2026, and the assembly is
heated at approximately 700.degree. C. to react Ni with W, whereby
the metal pattern is strongly bonded onto the AlN substrate
2021.
Next, as shown in FIG. 58, the light emitting element 2010 is
mounted on a predetermined position through gold bumps 2027, 2028.
The bump 2027 is connected to the n-electrode 2018 in the light
emitting element 2010, and the bump 2028 is connected to the
p-electrode 2016 in the light emitting element 2010. The light
emitting element 2010 in such a state as shown in FIG. 58 (a), the
light emitting element 2010 is surrounded by the metal pattern
2023.
Next, as shown in FIG. 59, a low melting glass sheet as the sealing
member is put on the surface side of the substrate 2021. This
assembly is heated in a reduced pressure atmosphere for fusing to
seal the light emitting element 2010, whereby Ni on the surface of
the metal pattern is strongly chemically bonded to the low melting
glass 2029 through the oxide on the Ni surface. Further, the
occurrence of residual air bubbles at the time of sealing can be
prevented.
When the light emitting element 2010 is of a flip chip type, the
bonding wire can be omitted. Also in this respect, the mechanical
stability is good. Thus, the optical device having the above
construction is suitable for a mass production process.
Finally, the substrate 2021 is divided at a parting line D to
provide the optical device of this example.
EXAMPLE 11
An optical device of another example is shown in FIGS. 60 to
63.
FIG. 60 is a plan view of this optical device. In this optical
device, the pattern on the substrate surface (mount face) side is
divided into a first part (a circular part) 2103 and a second part
(a bonded part) 2104, 2105. A plurality of holes 2107 are formed in
the first part 2103. An electrically conductive part 2108 extended
to the periphery of the substrate is formed in the first part 2103.
This electrically conductive part 2108 is used for the application
of an electric field during plating.
The first part 2103 is a laminate of a W layer and an Ni layer
formed in the same manner as in Example 10, and a strong bond among
substrate 2110--first part 2103--sealing member 2140 is provided by
applying an inorganic sealing member thereto. The second part 2104,
2105 of Cu formed by plating is extended through a first substrate
2111.
In the substrate 2110 in this example, Al.sub.2O.sub.3 is used as
the base material, and the first substrate 2111 is applied to the
second substrate 2112. AlN, glass-containing Al.sub.2O.sub.3 and
other inorganic materials may be used as the base material for each
of the substrates. The base material for the first substrate 2111
may be different from the base material for the second substrate
2112.
Through-holes 2107 are formed in the base material for the first
substrate 2111, and a metal layer in the first part 2103 as the
metal pattern is also stacked on circumferential face of the holes
2107.
Metal patterns 2120, 2121, 212 shown in FIG. 62 are formed on the
surface of the second substrate 2112. The circular metal pattern
2120 with a notch is located so as to face the hole 2107 in the
first substrate 111. As with the first part 2103 in the first metal
pattern, this metal pattern 2120 is formed of a laminate of a W
layer and a Ni layer. According to the metal pattern 2120 having
the above construction, a satisfactory strength of bonding to an
inorganic material (such as low melting glass) of the sealing
member which has entered the bottom of the hole 2107 can be
provided.
Metal patterns 2121, 2122 formed at the center of the second
substrate 2112 are provided at positions which face respectively to
the second parts 2104, 2105 in the metal pattern of the first
substrate 2111. When the first substrate 2111 is applied to the
second substrate 2112, the metal patterns 2121, 2122 are
electrically connected to the second parts 2104, 2105,
respectively. In the metal patterns 2121, 2122, an Au layer was
further stacked on a laminate of a W layer and a Ni layer. The
provision of the Au layer can improve the strength of bonding
between the metal patterns 2121, 2122 and the second parts 2104,
2105.
Through-holes 2125, 2126 are formed in the second substrate 2112.
Wide-area metal patterns 2131, 2132 are formed on the backside of
the second substrate 2112. The metal pattern 2121 on the surface
side of the second substrate 2112 is electrically connected to the
metal pattern 2131 on the backside through the electrically
conductive metal material filled into the through-hole 2125,
whereby the supply of electric power to or reception of electric
power from one of the electrodes in the element 2010 can be carried
out from the metal pattern 2131 through the metal pattern 2104 on
the surface of the first substrate 2111. Likewise, the metal
pattern 2122 on the surface side of the second substrate 2112 is
electrically connected to the metal pattern 2132 on the backside
through the electrically conductive metal material filled into the
through-hole 2126, whereby the supply of electric power to or
reception of electric power from the other electrode in the element
2010 can be carried out from the metal pattern 2132 through the
metal pattern 2105 on the surface of the first substrate 2111.
Electrically conductive parts 2135, 2136 are formed respectively in
the metal patterns 2131, 2132 formed on the backside of the second
substrate 2112. The electrically conductive parts 2135, 2136 are
used at the time of plating of the metal patterns 2131, 2132.
In the metal patterns 2131, 2132 on the backside of the second
substrate 2112, an Au layer was further stacked on a laminate of a
W layer and a Ni layer. The provision of the Au layer can improve
the strength of bonding between the metal patterns 2131, 2132 and
an external electrode. The metal material within the through-holes
2125 and 2126 is formed together with the formation of the metal
patterns 2131, 2132 and the metal patterns 2121, 2122 on the
surface side.
In this example, the first substrate 2111 is separately provided
from the second substrate 2112. They are then bonded to each other
to form an inorganic material substrate 2110. The first substrate
2111 and the second substrate 2112 are bonded to each other by any
method without particular limitation, for example, with the aid of
an adhesive.
When the substrate 2110 is divided, a metal pattern can be formed
in the parted face, resulting in improved degree of freedom of
circuit design. When the hole 2107 is extended through the
substrate 2110, in the case of some sealing member material, the
material is adhered to the lower mold supporting the substrate
2110, leading to a fear of deterioration in demolding. As in this
example, when the hole 2107 has a closed end, the contact between
the material for the sealing member and the lower mold can be
prevented. Further, when the hole 2107 is a through-hole, negative
pressure for releasing air between the sealing member and the
substrate surface cannot be applied to the whole area of the
substrate without difficulties. On the other hand, when the hole
2107 has a closed end, even in the case where air stays between the
sealing member and the substrate, air refuges in the hole, the
occurrence of air bubbles between the sealing member and the
substrate can be prevented. Clogging of one opening part in the
through-hole in the first substrate 2111 with the second substrate
2112 to form the closed-end hole 2107 is superior in mass
productivity to the formation of a closed-end hole in a single
timber.
The sealing member 2140 made of an inorganic light transparent
material is covered on the surface of the substrate 2110. The
material for the sealing member 2140 is of course strongly bonded
to the metal pattern 2103 on the surface of the substrate 2110,
and, at the same time, in this example, the material for the
sealing member 2140 sneaks in the hole 2107, resulting in physical
engagement between the material for the sealing member 2140 and the
substrate 2110, whereby, even when there is a large difference in
coefficient of thermal expansion between the sealing member 2140
and the substrate 2110, the deformation of both the materials can
be physically suppressed and, consequently, the separation of the
sealing member 2140 from the substrate 2110 can be more reliably
prevented.
Thus, since the provision of concaves and convexes on the substrate
surface covered by the sealing member can cause physical engagement
between the sealing member and the substrate, the separation of the
sealing member from the substrate can be more reliably prevented.
In addition to the closed-end hole of this example, a groove or
through-hole can also be used as the concave-convex. Further,
roughening of the substrate surface (Ra=not less than 0.5 .mu.m)
can realize physical engagement between both the materials. When
the surface of the base material in the substrate is roughened, the
roughness is reflected into the surface of the metal pattern when
the metal pattern is formed on the substrate. Further, the
concave-convex can also be formed by providing holes only in the
metal pattern 2103, that is, the formation of the metal pattern
2103, for example, in a lattice form.
The action of the concave-convex is also effective in the case
where the sealing member made of an inorganic light transparent
material is covered directly on the base material of the inorganic
material substrate without through any metal pattern.
FIG. 64 shows an example in which a closed-end hole 2257 is formed
in the substrate of the optical element of Example 10. As shown in
FIGS. 64 and 60, preferably the holes, that is, concaves-convexes,
are evenly distributed on the surface of the substrate from the
viewpoint of ensuring engagement between the sealing materials and
the concaves-convexes in the whole area of the substrate surface to
prevent the separation of the sealing material from the
concave-convex.
Embodiments shown in FIGS. 65 to 74 will be explained in
detail.
(Optical Element)
Optical elements include light emitting diodes, laser diodes, and
other light emitting elements and photodetectors. The wavelength of
light to be received and the wavelength of light to be emitted in
the optical element are not particularly limited, and, for example,
group III nitride-based compound semiconductor elements useful for
lights ranging from ultraviolet light to green light, and
GaAs-based semiconductor elements useful for red lights may be
used. Other optical elements usable herein include those made of
SiC, AlInGaP and the like.
Group III nitride-based compound semiconductor light emitting
elements which emit short wavelengths pose a significant problem
associated with the sealing member. Group III nitride-based
compound semiconductors are represented by general formula
Al.sub.XGa.sub.YIn.sub.1-X-YN where 0<X.ltoreq.1,
0.ltoreq.Y.ltoreq.1, and 0.ltoreq.X+Y.ltoreq.1. Among them,
Al-containing group III nitride-based compound semiconductors
include the so-called binary systems of AlN, and the so-called
ternary systems of Al.sub.xGa.sub.1-xN and Al.sub.xIn.sub.1-xN
where 0<x<1. In the group III nitride-based compound
semiconductors and GaN, at least a part of the group III elements
may be replaced with boron (B), thallium (Tl) or the like. At least
a part of nitrogen (N) may also be replaced with phosphorus (P),
arsenic (As), antimony (Sb), bismuth (Bi) or the like.
The group III nitride-based compound semiconductor may contain any
dopant. n-type impurities usable herein include silicon (Si),
germanium (Ge), selenium (Se), tellurium (Te), and carbon (C).
p-type impurities usable herein include magnesium (Mg), zinc (Zn),
beryllium (Be), calcium (Ca), strontium (Sr), and barium (Ba).
After doping with the p-type impurity, the group III nitride-based
compound semiconductor may be exposed to electron beams, plasma, or
heat in an oven. This, however, is not indispensable.
The group III nitride-based compound semiconductor layer is formed
by an MOCVD (metal-organic vapor phase epitaxy) method. All the
semiconductor layers constituting the element are not always
required to be formed by the MOCVD method, and the MOCVD method may
be used in combination with a molecular beam epitaxy method (MBE
method), a halide vapor-phase epitaxy method (HVPE method),
sputtering, ion plating or the like.
Regarding the construction of the light emitting element, a homo
structure, hetero structure, or double hetero structure with MIS
junction, PIN junction or pn junction may be adopted. In the light
emitting layer, a quantum well structure (a single quantum well
structure or a multiple quantum well structure) may also be
adopted. The group III nitride-based compound semiconductor light
emitting element may be of a face-up type in which the main light
receiving/emitting direction (electrode face) is an optical axis
direction in the optical device, and a flip-chip type in which the
main light receiving/emitting direction is a direction opposite to
the optical axis direction and reflected light is utilized.
The epitaxial growth temperature of the group III nitride-based
compound semiconductor element is about 1050.degree. C., and,
regarding the epitaxial growth temperature of the GaAs-based
semiconductor element, the heat resistant temperature is
600.degree. C. or above. In both the cases, the use of low melting
glass can realize processing without heat damage.
(Inorganic Material Substrate)
In the optical device of this invention, the above-mentioned
optical element is mounted on an inorganic material substrate. The
base material and the form of the inorganic material substrate may
be properly selected depending upon applications of the optical
device. For example, rectangular plates of AlN, Al.sub.2O.sub.3,
glass-containing Al.sub.2O.sub.3 or the like may be used.
Any substrate may be used so far as at least the surface of the
substrate is made of the base material. For example, a substrate
may be used in which the center part is made of Al or Al alloy, and
the surface thereof is surrounded by AlN.
(Metal Pattern)
A first metal pattern and a second metal pattern are formed on an
inorganic material substrate.
The first metal pattern electrically connects each electrode in the
optical element to an external circuit, whereby electric power is
received from and supplied to the optical element. Specifically,
when the optical element is a light emitting element, electric
power is applied to the optical element from the external circuit.
On the other hand, when the optical element is a photodetector,
electric power generated in the optical element is taken out to the
external circuit.
The second metal pattern functions as an adhesive layer for stably
bonding the inorganic sealing member to the inorganic material
substrate. Since the sealing member is disposed so as to surround
the optical element, the second metal pattern is also disposed so
as to surround the first metal pattern on which the optical element
is mounted. This can maximize the area of the second metal pattern
interposed between the sealing member and the inorganic material
substrate. The second metal pattern is not limited to a continuous
pattern and may be noncontinuous.
The first metal pattern may be continuous to the second metal
pattern. When the first metal pattern is insulated from the second
metal pattern, however, electric field plating of materials optimal
for respective functions can be carried out by independently
applying the electric field.
The metal layer also functions to reflect light, and, thus, light
from the optical element can be fully reflected to improve light
takeout efficiency by surrounding the optical element with the
first metal pattern and the second metal pattern. For example, a
black substrate of AlN disadvantageously absorbs light from the
optical element, and a substrate of Al.sub.2O.sub.3 is
disadvantageously transparent to light emitted from the optical
element. In this case, when the optical element is surrounded by
the metal pattern, the light from the optical element can be
efficiently reflected from the metal pattern and can be led to the
outside of the device.
In order to improve reflection efficiency of light, preferably, the
surface of the first metal pattern formed closer to the optical
element is made of a metal layer with a high refractive index such
as an Ag layer or the like.
In the material for first metal pattern formation, the surface
layer should be compatible with a bonding material for bonding the
optical element. For example, when Au bumps are used as the bonding
material, the surface layer in the first metal pattern is made of
Au or Ag. Layers other than the surface layer are preferably made
of a material common to these layers and the second metal pattern
from the viewpoint of improving productivity.
In addition to Au bumps, eutectic materials such as solder bumps
and solder plating can be used as a bonding material for bonding
the optical element to the substrate.
The Ag layer has high light reflectance and, thus, in the first
metal pattern, is preferably partially formed in the site on the
periphery of the optical element.
The material for the second metal pattern formation is properly
selected depending upon the material for the sealing member and the
material for the inorganic material substrate so that the material
for metal pattern formation is bonded with good boding strength to
the sealing member and the inorganic material substrate. The metal
pattern may have a multilayered structure. For example, W, W\Ni (Ni
being stacked on W), W\Ni\Ag (Ni and Ag being stacked in that order
on W), and copper foils (strength of bonding to the
glass-containing Al.sub.2O.sub.3 substrate can be provided through
an oxide, and the substrate has a coefficient of thermal expansion
(13.times.10.sup.-6 (1/.degree. C.)) close to the inorganic sealing
member) may be adopted as the material for metal pattern
formation.
Upon heating, the W layer enters in a wedge form into the sealing
member and the inorganic material in the substrate to form strong
bonding between the sealing member and the inorganic material in
the substrate. When the Ni layer is formed on the W layer, upon
heating, a chemical bond is formed between the Ni layer and the
sealing member, whereby the Ni layer and the sealing member are
strongly boned to each other.
The surface of the second metal pattern is preferably made of a
material having good wettability by the sealing member in a
softened state. At least one of Ni, Cr, Ti, Cu or alloys thereof
may be mentioned as this type of material.
The second metal pattern for joining the substrate surface to the
sealing member is preferably formed in the largest possible area on
the substrate surface.
The second metal pattern which should occupy a large area on the
substrate surface is preferably made of a material having a
coefficient of thermal expansion intermediate between the
coefficient of thermal expansion of the sealing member (coefficient
of thermal expansion: small) and the coefficient of the thermal
expansion of the inorganic material substrate (coefficient of
thermal expansion: large). This can reduce the difference in
coefficient of thermal expansion between the sealing member and the
inorganic material substrate. Upon cooling of the high temperature
state adopted in covering optical element with the sealing member
to room temperature, the sealing member and the inorganic material
substrate are shrunken on a level depending upon the coefficient of
thermal expansion of each of the sealing member and the inorganic
material substrate. When there is a significant difference in
coefficient of thermal expansion between the sealing member and the
inorganic material substrate, however, there is a fear of causing
deformation of the substrate or separation of the sealing member
from the substrate. The interposition of a second metal pattern
intermediate between the coefficient of the substrate and the
coefficient of the sealing member can relax stress based on the
difference in coefficient of thermal expansion between the
substrate and the sealing member.
When the sealing member and the substrate are made of low melting
glass and AlN, respectively, the coefficient of thermal expansion
is 17.3.times.10.sup.-6/.degree. C. for low melting glass and
4.5.times.10.sup.-6/.degree. C. for AlN. In this case, Ni
(coefficient of thermal expansion: 12.8.times.10.sup.-6/.degree.
C.) having a coefficient of thermal expansion intermediate between
the sealing member and the substrate is preferably adopted as a
material for metal pattern formation.
From the viewpoint of reducing the thermal deformation level of the
substrate, the formation of the second metal pattern on a large
area of the optical element mount face (surface) of the substrate
is preferred. More preferably, a metal pattern made of an identical
or similar material is also formed in a large area on the backside
of the substrate to further suppress the thermal deformation of the
substrate.
In forming the metal pattern material on the substrate surface so
as to extend to the backside of the substrate, the pattern on the
substrate surface can be connected to the pattern on the backside
of the substrate by providing a through-hole (via hole) in the
substrate and filling the material for the metal pattern into the
through-hole. Since the electric terminal is drawn from the optical
element mount face of the substrate to the backside, there is no
particular need to provide a portion, not covered by the sealing
member of the optical element, for the electric terminal on the
optical element mount face side of the substrate and the whole area
can be sealed with a sealing member sheet. Therefore, the mass
productivity is excellent. In this case, when no through-hole is
provided in the substrate, the sealing member of the optical
element on the optical element mount face side does not reach the
backside. When the through-hole is formed on the optical element
mount position, the heat from the optical element can be released
to the outside of the device through the metal pattern material
within the through-hole. This can improve heat dissipation
efficiency and is particularly suitable for the group III
nitride-based compound semiconductor light emitting element having
a large calorific value.
The method for first and second metal pattern formation is not
particularly limited. In the working example, however, a paste of W
was screen printed on an inorganic material substrate, and the
print was then fired to form a metal pattern of W on the inorganic
material substrate. This W layer was plated with a Ni layer to form
a metal pattern of W\Ni, followed by heat treatment. In the case of
W\Ni\Ag, the Ni layer formed by plating is further plated with
Ag.
Alternatively, these metal layers may be formed by sputtering or
other well known methods.
A metallic thin film such as a Cu foil can also be bonded onto the
backside of the substrate where a complicated and accurate pattern
form is not required.
(Sealing Member)
The inorganic sealing member is not particularly limited so far as
it is transparent to the wavelength of received or emitted light in
the optical element and can protect the optical element. When the
fact that the heat resistant temperature of the optical element is
about 600.degree. C. is taken into consideration, however, the
adoption of low melting glass having a melting point (softening
point) below the heat resistant temperature is preferred.
In addition to lead glass and chalcogenide glass,
SiO.sub.2--Nb.sub.2O.sub.5-based, B.sub.2O.sub.3--F-based,
P.sub.2O.sub.5--F-based, P.sub.2O.sub.5--ZnO-based,
SiO.sub.2--B.sub.2O.sub.3--La.sub.2O.sub.3-based or
SiO.sub.2--B.sub.2O.sub.3-based glasses may be adopted as the low
melting glass. All of these low melting glasses can be pressed at
350 to 600.degree. C.
A fluorescent material can also be dispersed in the sealing member.
An inorganic fluorescent material powder can be used as the
fluorescent material and can be mixed into the low melting glass.
Further, rare earth ions can be doped into the low melting glass to
yield fluorescence. A proper combination of a light emitting
element with a fluorescent material can produce desired luminescent
colors including white light.
In the combination of the sealing member with the optical element,
preferably, the Abbe number of the sealing member is 40 or less,
the refractive index is 1.6 or more, and the wavelength of light
reception and light emission of the optical element is brought to
not more than 546.1 nm (wavelength of e radiation of Na).
Specifically, regarding the external quantum efficiency of light
emitted within the high refractive index material, a higher
refractive index of the sealing material with respect to the
wavelength of emitted light is more advantageous. The refractive
index of the optical material is defined by d radiation of Na. In
general, the refractive index increases with reducing the
wavelength, and the level of a change in refractive index as a
function of light wavelength is indicated by the Abbe number. In
particular, in the light emitting element of short wavelength
emission which poses a problem associated with the conventional
resin sealing, selecting a material which is high in refractive
index in d radiation of Na and causes a significant change in
refractive index with respect to the wavelength can prevent a
lowering in output of light caused by yellowing of the resin. In
addition, in essence, regarding short wavelength light, sealing
with a high refractive index material can be realized, and high
external quantum efficiency can be provided.
SiO.sub.2--Nb.sub.2O.sub.5-based glass may be mentioned as the low
melting glass having the above optical properties. Among others,
SiO.sub.2--Nb.sub.2O.sub.5--Na.sub.2O glass is preferred.
When a sealing member of a low melting glass sheet is put on an
optical element followed by heating for softening, the light
emitting element can be surrounded by the sealing member. This
heating is preferably carried out under a reduced pressure
atmosphere to prevent the entry of air into between the sealing
member and the optical element. Upon heating, a chemical reaction
takes place at the interface of the low melting glass and the
second metal pattern, whereby both the materials are strongly
bonded to each other.
Concaves-convexes may be formed in the sealing member in a softened
state put on top of the optical element. For example, a concave
part (thin thickness part) can be provided in the sealing member
along the splitting line of the inorganic material substrate to
facilitate the splitting work. Further, in this case, the sealing
member is formed in a fine lattice form by convex parts
corresponding to chips and concaves along the splitting lines. The
thermal deformation does not correspond to the size of the sheet
before concave-convex formation but to the size of the fine
lattice, and, thus, the thermal deformation of the sealing member
can be reduced. Even when there is a significant difference in
coefficient of thermal expansion between the sealing member and the
substrate, the separation between the substrate and the sealing
member can be prevented. Further, a problem of the warpage of the
substrate can be reduced.
When the convex part of the sealing member is formed in a convex
lens form, light from the light emitting element can be allowed to
focus in an optical axis direction. Further, light from the outside
of the device can be allowed to focus on the photodetector. In this
case, a high refractive index material is preferably used as the
material for the sealing member.
The sealing member in a softened state is preferably applied to the
optical element under the reduced pressure from the viewpoint of
preventing air from being trapped within the sealing member.
Concaves and convexes in the sealing member can be formed by
applying a sealing member sheet to the optical element and then
pressing the assembly during a period in which the sealing member
is maintained in a softened state, or reheating the assembly to
soften the sealing member for pressing.
This invention will be explained with reference to the following
examples.
EXAMPLE 12
In this example, a flip chip-type group III nitride-based compound
semiconductor light emitting element 3010 shown in FIG. 65 was used
as an optical element. This light emitting element emits blue
light.
The specifications of each layer constituting the light emitting
element 3010 are as follows.
TABLE-US-00003 Layers Composition p-type layer 3015 p-GaN:Mg Layer
3014 including light Including InGaN layer emitting layer n-type
layer 3013 n-GaN:Si Buffer layer 3012 AlN Substrate 3011
Sapphire
The n-type layer 3013 made of GaN doped with Si as an n-type
impurity is formed on the substrate 3011 through the buffer layer
3012. In this example, sapphire is used as the substrate 3011. The
material for the substrate 3011, however, is not limited to
sapphire, and examples of materials usable herein include sapphire,
spinel, silicon carbide, zinc oxide, magnesium oxide, manganese
oxide, zirconium boride, and group III nitride-based compound
semiconductor single crystals. The buffer layer is formed by MOCVD
using AlN. The material for the buffer layer, however, is not
limited to AlN, and other materials such as GaN, InN, AlGaN, InGaN
and AlInGaN may also be used. For example, a molecular beam epitaxy
method (MBE method), a halide vapor-phase epitaxy method (HVPE
method), sputtering, or ion plating may be used for the formation
of the buffer layer. When the substrate is made of a group III
nitride-based compound semiconductor, the provision of the buffer
layer can be omitted.
The substrate and the buffer layer can be if necessary removed
after semiconductor element formation.
In this example, the n-type layer 3013 is made of GaN.
Alternatively, the n-type layer 3013 may be made of AlGaN, InGaN or
AlInGaN.
Further, the n-type layer 3013 has been doped with Si as an n-type
impurity. Other n-type impurities usable herein-include Ge, Se, Te,
and C.
The layer 3014 including a light emitting layer may comprise a
quantum well structure (a multiple quantum well structure or a
single quantum well structure), and the structure of the light
emitting element may be of single hetero type, double hetero type,
and homojunction type.
The layer 3014 including a light emitting layer may also include,
on its p-type layer 3015 side, a group III nitride-based compound
semiconductor layer with a broad bandgap doped with Mg or the like.
This can effectively prevent electrons injected into the layer 3014
including a light emitting layer from diffusing into the p-type
layer 3015.
The p-type layer 3015 made of GaN doped with Mg as a p-type
impurity is formed on the layer 3014 including a light emitting
layer. The p-type layer 3015 may also be made of AlGaN, InGaN or
InAlGaN. Zn, Be, Ca, Sr, or Ba may also be used as the p-type
impurity. After the introduction of the p-type impurity, the
resistance can be lowered by a well-known method such as electron
beam irradiation, heating in an oven, or plasma irradiation.
In the light emitting element having the above construction, each
group III nitride-based compound semiconductor layer may be formed
by MOCVD under conventional conditions, or alternatively may be
formed by a method such as a molecular beam epitaxy method (MBE
method), a halide vapor-phase epitaxy method (HVPE method),
sputtering, or ion plating.
An n-electrode 3018 has a two-layer structure of an Al layer and a
V layer. After the formation of the p-type layer 3015, the p-type
layer 15, the layer 3014 including a light emitting layer, and a
part of the n-type layer 3013 are removed by etching to expose the
n-type layer 3013, and the n-electrode 3018 is formed by vapor
deposition on the exposed n-type layer 3013.
A p-electrode 3016 is stacked on the p-type layer 3015 by vapor
deposition. After the formation of the individual layers and
electrodes by the above steps, the step of isolating chips is
carried out.
Next, an inorganic material substrate for mounting the light
emitting element 3010 is provided.
A base material for an inorganic material substrate 3021 in this
example is AlN, and metal patterns 3023, 3024 are provided on
respective upper and lower sides thereof. As shown in FIG. 66, the
upper pattern 3023 comprises first metal patterns 3025n, 3025p and
a second metal pattern 26. The first metal pattern 3025n is
connected to the optical element 3010 in its n-electrode 3018
through the Au bump 3027. The first metal pattern 3025p is
connected to the optical element in its p-electrode 3016 through an
Au bump 3028. As shown in FIG. 67, the first metal pattern 25n is
electrically connected to the metal pattern 3024n on the backside
of the substrate through a through-hole 3031 formed in the base
material of the inorganic material substrate 3021. Likewise, the
first metal pattern 3025p is electrically connected to a metal
pattern 3024p on the backside of the substrate through a
through-hole 3032. As shown in FIG. 68 (an enlarged view of the
principal part of FIG. 67), the through-holes 3031, 3032 are filled
with Cu by plating.
The second metal pattern 3026 is elongated from the first metal
patterns 3025n, 3025p and is formed in a circular region
surrounding the first metal patterns 3025n, 3025p.
As shown in FIG. 69, the metal patterns 3024n and 3024p on the
backside are preferably formed in the largest possible area. Thus,
the deformation level of the substrate 3021 upon exposure to heat
history can be brought to a value closer to the deformation level
of the sealing member 3029 by bonding of the large-area pattern
made of a metal material having a coefficient of thermal expansion
intermediate between the sealing member and the substrate to the
backside of the substrate 3021. Therefore, the warpage of the
substrate 3021 and the separation between the sealing member and
the substrate can be more reliably prevented.
Each metal pattern is formed as follows. At the outset, a
W-containing paste is coated on both sides of the inorganic
material substrate 3021 with through-holes before firing and the
through-holes, for example, by screen printing. Thereafter, AlN is
sintered at a temperature above 1500.degree. C., and the W paste is
baked onto the substrate 3021, whereby W is strongly bonded to the
substrate. This W can also be formed by sputtering. Alternatively,
instead of W, a high melting metal such as Mo may be used.
Next, a Ni layer is formed on the W pattern by plating, followed by
heating at about 700.degree. C. to react Ni with W, whereby the
metal pattern is strongly bonded onto the AlN substrate 3021.
Ni is strongly chemically bonded to the sealing member made of an
inorganic light transparent material. Since the inorganic material
for the sealing member in a softened state has good wettability by
Ni, the material for the sealing member comes into contact with the
whole area of the second electrode pattern to prevent the
occurrence of air bubbles and, at the same time, high bonding
strength can be provided between the sealing member and the second
electrode pattern.
In the first metal patterns 3025n, 3025p, preferably, good bonding
to the top of the Ni layer through Au bumps can be realized, and a
high reflectance Ag layer is formed. When light emitting element
has a reflective face on its bottom, taking into consideration only
bonding through Au bumps suffices for good results, and, for
example, with respect to a blue light emitting element, an Au layer
may be formed on the Ni layer.
Since through-holes 3031, 3032 are formed on positions just under
the first metal patterns 3025n, 3025p, heat from the optical
element 10 can be efficiently released to the outside of the device
(backside of the substrate 3021) through the metal material within
the through-holes.
Next, as shown in FIG. 67, the light emitting element 3010 is
mounted at a predetermined position through Au bumps 3027, 3028.
The bump 3027 is connected to the light emitting element 3010 in
its n-electrode 3018, and the bump 3028 is connected to the light
emitting element 3010 in its p-electrode 3016. In such a state as
shown in FIG. 66, the light emitting element 3010 is surrounded by
the first metal patterns 3025n and 3025p.
Next, as shown in FIG. 67, a low melting glass sheet as the sealing
member is put on the surface side of the substrate 3021, and the
assembly is heated in a reduced pressure atmosphere to fuse the low
melting glass to the substrate 3021, thereby sealing the light
emitting element 3010. Thus, Ni on the surface of the metal pattern
and the low melting glass 3039 are chemically and strongly bonded
to each other through an oxide on the Ni surface. Further, the
occurrence of residual air bubbles at the time of sealing can be
prevented.
When the low melting glass sheet has softened, preferably, the
assembly is pressed to form concaves and convexes thereon. The
concave part in the sealing member 3039 is allowed to conform to
the splitting line 3037 (notch) in the substrate 3021, the
substrate splitting work becomes easy. The convex part in the
sealing member 3039 is preferably in a lens form to improve light
takeout efficiency.
In the above series of production process, the light emitting
element 3010 is connected to the first metal patterns 3025n and
3025p through gold bumps 3027, 3028 having a melting point above
the processing temperature, and, thus, there is no fear of causing
the bumps 3027, 3028 to be softened by the sealing temperature.
Therefore, even when force is applied to the light emitting element
during sealing work, the position of the light emitting element
3010 is not deviated from the predetermined position. When a flip
chip-type light emitting element is adopted as the light emitting
element 3010, the provision of the bonding wire is omitted. Also in
this point, mechanical stability is ensured. Therefore, it can be
said that the optical device having the above construction is
suitable for a mass production process.
Further, the coefficient of thermal expansion of the Ni layer
occupying a major part of the layer thickness of the metal pattern
is 12.8.times.10.sup.-6/.degree. C. which is intermediate between
the coefficient of thermal expansion of AlN
(4.5.times.10.sup.-6/.degree. C.) and the coefficient of thermal
expansion of low melting glass 3039 (17.3.times.10.sup.-6/.degree.
C.).
Thus, the interposition of the metal pattern between the inorganic
sealing member 3039 and the inorganic material substrate 3021 can
realize a strong bond between the sealing member 3039 and the
substrate 3021 and, at the same time, can reduce stress caused by a
difference in coefficient of thermal expansion between the sealing
member 3039 and the substrate 3021. Therefore, unfavorable
phenomena such as warpage and cracking in the substrate 3021 and
separation of the sealing member 3039 from the substrate 3021 can
be reliably prevented.
Finally, the substrate 3021 is split in the splitting line 3037 to
provide optical devices of this example.
Variants of this example are shown in FIGS. 70 to 73. In FIG. 22
and FIGS. 70 to 73, like parts are identified with the same
reference characters, and the explanation thereof will be
omitted.
In the optical device shown in FIG. 69, the second metal pattern
3041 is in a rectangular circular form.
In the optical device shown in FIG. 70, the second metal pattern 43
is noncontinuous.
In the example shown in FIG. 72, instead of the sapphire substrate,
a GaN substrate 3011a or SiC was adopted as the substrate for the
flip chip-type light emitting element. Since the substrate for the
element has a higher refractive index than the sapphire substrate,
combining this substrate with a high refractive index sealing
member (such as low melting glass) can improve light takeout
efficiency.
Chamfering the peripheral part of the GaN substrate 3011a can
further improve the efficiency of light takeout from the optical
element 3010.
Further, in the example shown in FIG. 72, Al.sub.2O.sub.3 which has
a larger coefficient of thermal expansion (coefficient of thermal
expansion: 6.7.times.10.sup.-6) and is more inexpensive than AlN
was adopted as the base material for the inorganic material
substrate 3051.
In the example shown in FIG. 73, glass-containing Al.sub.2O.sub.3
was adopted as the base material for the inorganic material
substrate 3061. Further, a Cu foil was adhered to the whole area of
the substrate 3061. Cu was filled into the through-holes 3031 and
3032 by plating. Upon heating of the inorganic material substrate
3061 to 1000.degree. C., Cu is chemically bonded to
Al.sub.2O.sub.3. The formation of a Cu layer, having a coefficient
of thermal expansion similar to the glass, in a large area on the
backside of the glass-containing Al.sub.2O.sub.3 substrate can
prevent problems of the warpage of the substrate and the separation
between the sealing member and the substrate.
The base (Cu foil) for the first metal pattern is identical to the
base (Cu foil) for the second metal pattern, and only light
emitting element mount areas 3025n, 3025p are plated with Ag and
Au. This can be easily carried out by masking the second metal
pattern area.
For example, a construction may be adopted in which an identical
base Cu foil is plated with Ni, and, with respect to a blue light
emitting element, a reflective layer of a second metal pattern may
be provided. Thus, the first metal patterns 3025n, 3025p may not be
separated from the second metal pattern 3026.
EXAMPLE 13
An optical device of this example is shown in FIG. 74. A light
emitting element 3100 used in this example is of a type which has
an-electrode in its upper and lower parts. Therefore, the provision
of the bonding wire 3101 is necessary.
A through-hole 3111 is formed in the inorganic material substrate
3110 made of AlN, and Cu is filled into the through-hole 3111 by
plating. A metal pattern of W\Ni is formed in a large area on both
sides of the substrate 3110. This metal pattern is formed in the
same manner as in Example 12.
One electrode in the light emitting element 3100 is mounted on the
first metal pattern 3113a on the through-hole 3111 from the
viewpoint of improving heat lead-out efficiency. A bonding wire
3101 is drawn from the other electrode and is bonded to the second
metal pattern 3113b.
On the other hand, a spacer sheet 3120 made of low melting glass is
provided. Holes within which the light emitting element 3100 and
the bonding wire 3101 are placed are formed in the spacer 3120. The
spacer 3120 may be put on top of the substrate 3110 without
interference to the light emitting element 3100 and the bonding
wire 3101 (state shown in FIG. 74). In this state, a sealing member
3130 made of low melting glass is mounted. In this case, there is a
fear of causing the bonding wire 3101 to be deformed by the
material for the sealing member. This deformation, however, is
regulated by the spacer 3120. Therefore, cutting or
short-circuiting of the bonding wire 3101 can be prevented.
From the viewpoint of protecting the bonding wire 3101, preferably,
the spacer 3120 sneaks to the lower side of the bonding wire
3101.
Next, embodiments shown in FIGS. 75 to 83 will be explained in
detail.
(Light Emitting Element)
Light emitting elements include light emitting diodes, laser
diodes, and other light emitting elements. The emission wavelength
of the light emitting element is not particularly limited. For
example, group III nitride-based compound semiconductor elements
useful for lights ranging from ultraviolet light to green light,
and GaAs-based semiconductor elements useful for red lights may be
used. Other light emitting elements usable herein include those
made of SiC, AlInGaP and the like.
As described above, the group III nitride-based compound
semiconductor light emitting element provided with an insulating
substrate has a problem associated with waste heat. When this light
emitting element is used, for example, as a white light source,
high output is particularly required.
Group III nitride-based compound semiconductors are represented by
general formula Al.sub.XGa.sub.YIn.sub.1-X-YN where
0<X.ltoreq.1, 0.ltoreq.Y.ltoreq.1, and 0.ltoreq.X+Y.ltoreq.1.
Among them, Al-containing group III nitride-based compound
semiconductors include the so-called binary systems of AlN, and the
so-called ternary systems of Al.sub.xGa.sub.1-xN and
Al.sub.xIn.sub.1-xN where 0<x<1. In the group III
nitride-based compound semiconductors and GaN, at least a part of
the group III elements may be replaced with boron (B), thallium
(Tl) or the like. At least a part of nitrogen (N) may also be
replaced with phosphorus (P), arsenic (As), antimony (Sb), bismuth
(Bi) or the like.
The group III nitride-based compound semiconductor may contain any
dopant. n-type impurities usable herein include silicon (Si),
germanium (Ge), selenium (Se), tellurium (Te), and carbon (C).
p-type impurities usable herein include magnesium (Mg), zinc (Zn),
beryllium (Be), calcium (Ca), strontium (Sr), and barium (Ba).
After doping with the p-type impurity, the group III nitride-based
compound semiconductor may be exposed to electron beams, plasma, or
heat in an oven. This, however, is not indispensable.
The group III nitride-based compound semiconductor layer is formed
by an MOCVD (metal-organic vapor phase epitaxy) method. All the
semiconductor layers constituting the element are not always
required to be formed by the MOCVD method, and the MOCVD method may
be used in combination with a molecular beam epitaxy method (MBE
method), a halide vapor-phase epitaxy method (HVPE method),
sputtering, ion plating or the like.
Regarding the construction of the light emitting element, a homo
structure, hetero structure, or double hetero structure with MIS
junction, PIN junction or pn junction may be adopted. In the light
emitting layer, a quantum well structure (a single quantum well
structure or a multiple quantum well structure) may also be
adopted. The group III nitride-based compound semiconductor light
emitting element may be of a face up-type in which the main light
emitting direction (electrode face) is an optical axis direction in
the luminescent device, and a flip chip-type in which the main
light emitting direction is a direction opposite to the optical
axis direction and reflected light is utilized.
(Submount)
The base material for the submount may be properly selected
depending upon the applications of the luminescent device so far as
it is highly thermally conductive. For example, inorganic materials
such as AlN, Al.sub.2O.sub.3, SiC, Si.sub.3N.sub.4, and Si may be
selected.
The inorganic material for the formation of the submount has a
coefficient of thermal expansion intermediate between the
semiconductor material in the light emitting element and the metal
material in the lead frame. Accordingly, even when large heat
history is applied during the manufacturing process of the
luminescent device (for example, when the submount is soldered to
the first and second lead frames), the stress caused by the
coefficient of thermal expansion of the light emitting element and
the lead frame can be relaxed.
The submount may be in any form so far as one end of the submount
can be set in a first concave part formed in the first lead frame,
and the other end can be set in a second concave part formed in the
second lead frame.
When a flip chip-type light emitting element is adopted, the wire
is omitted. Accordingly, the application of a large current to the
light emitting element becomes possible. Consequently,
high-brightness emission of the light emitting element can be
realized and, in addition, the heat of the light emitting element
can be efficiently dissipated. Further, the omission of the wire
can improve the impact resistance of the luminescent device.
Instead of the wire, a wiring pattern such as a through-hole or a
side metal is formed in the submount. Each electrode in the light
emitting element mounted on the upper surface of the submount is
electrically connected through this wiring pattern to the first
lead frame and the second lead frame. The surface layer in the
material for metal pattern formation should be compatible with the
bonding material for bonding the light emitting element. For
example, when Au bumps are used as the bonding material, the
surface layer of the metal pattern is made of Au or Ag.
In addition to the Au bump, eutectic materials such as solder bumps
or solder plating may be used as a bonding material for bonding the
light emitting element to the wiring pattern in the submount.
(First Lead Frame and Second Lead Frame)
The first concave part is formed at the one end of the first lead
frame, and the second concave part is formed at one end of the
second lead frame. The first concave part and the second concave
part can be formed by forming a groove by cutting or etching in the
thickness-wise direction in the first and second lead frames.
Alternatively, the first and second concave parts may be formed by
pressing the material for the first lead frame and the material for
the second lead frame. A method may also be adopted in which convex
parts are provided on the surface of the first and second lead
frames and a part surrounded by the convex parts is used as the
concave part.
The concave part functions as a receiving seat for the submount,
and the shape and the depth thereof are properly designed according
to the submount.
One end of the submount is set to the first concave part, and the
other end is set to the second concave part. The submount and the
first and second lead frames are mechanically fixed, for example,
by solder (for example, Pb--Sn or Au--Sn) or Ag paste made of a
metallic eutectic material.
The submount mounting position is stabilized by reducing the margin
between the submount and the peripheral wall of the first and
second concaves, for example, when the submount and the first and
second concave parts are in a substantially fitted state, whereby
displacement of the light emitting element can be prevented. Thus,
light distribution characteristics in the case where the light
emitting element has been sealed with a lens-shaped sealing member
are stabilized.
In such a state that the submount is set in the first and second
concaves, when the submount is substantially level with the height
of the first and second lead frames, light released laterally from
the light emitting element can be easily controlled to improve the
light takeout efficiency.
Further, when the submount is substantially level with the height
of the first and second lead frames and the gap between the
submount and the first and second lead frames is small (fitted
state), that is, when the submount and the first and second lead
frames are substantially flush with each other, the efficiency of
reflection by the lead frames can also be improved.
This invention will be explained with reference to the following
examples.
A light emitting element 10 is a group III nitride-based compound
semiconductor light emitting element. FIG. 75 is a typical diagram
showing the construction of this element. As shown in FIG. 75, in
the light emitting element 4010, a plurality of group III
nitride-based compound semiconductor layers are stacked on a
sapphire substrate. Specifications of each layer constituting the
light emitting element 4010 are as follows.
TABLE-US-00004 Layers Composition p-type semiconductor layer
p-GaN:Mg 4015 Layer 4014 including light Including InGaN layer
emitting layer n-type semiconductor layer n-GaN:Si 4013 Buffer
layer 4012 AlN Substrate 11 Sapphire
The n-type semiconductor layer 4013 made of GaN doped with Si as an
n-type impurity is formed on the substrate 4011 through the buffer
layer 4012. In this example, sapphire is used as the substrate
4011. The material for the substrate 4011, however, is not limited
to sapphire, and examples of materials usable herein include
sapphire, spinel, silicon, silicon carbide, zinc oxide, gallium
phosphide, gallium arsenide, magnesium oxide, manganese oxide, and
group III nitride-based compound semiconductor single crystals. The
buffer layer is formed by MOCVD using AlN. The material for the
buffer layer, however, is not limited to AlN, and other materials
such as GaN, InN, AlGaN, InGaN and AlInGaN may also be used. For
example, a molecular beam epitaxy method (MBE method), a halide
vapor-phase epitaxy method (HVPE method), sputtering, ion plating
or electron shower may be used for the formation of the buffer
layer. When the substrate is made of a group III nitride-based
compound semiconductor, the provision of the buffer layer can be
omitted.
The substrate and the buffer layer can be if necessary removed
after semiconductor element formation.
In this example, the n-type semiconductor layer 4013 is made of
GaN. Alternatively, the n-type semiconductor layer 4013 may be made
of AlGaN, InGaN or AlInGaN.
Further, the n-type semiconductor layer 4013 has been doped with Si
as an n-type impurity. Other n-type impurities usable herein
include Ge, Se, Te, and C.
The n-type semiconductor layer 4013 may have a two-layer structure
of a low-electron concentration n layer on the side of a layer 4014
including a light emitting layer and a high electron concentration
n+ layer on the side of a buffer layer 12.
The layer 4014 including a light emitting layer may comprise a
quantum well structure (a multiple quantum well structure or a
single quantum well structure), and the structure of the light
emitting element may be of single hetero type, double hetero type,
and homojunction type.
The layer 4014 including a light emitting layer may also include,
on its p-type semiconductor layer 4015 side, a group III
nitride-based compound semiconductor layer with a broad bandgap
doped with an acceptor such as Mg or the like. This can effectively
prevent electrons injected into the layer 4014 including a light
emitting layer from diffusing into the p-type layer 4015.
The p-type semiconductor layer 4015 made of GaN doped with Mg as a
p-type impurity is formed on the layer 4014 including a light
emitting layer. The p-type semiconductor layer 4015 may also be
made of AlGaN, InGaN or InAlGaN. Zn, Be, Ca, Sr, or Ba may also be
used as the p-type impurity.
Further, the p-type semiconductor layer 4015 may have a two-layer
structure of a low hole concentration p-layer on the side of the
layer 4014 including a light emitting layer and a high hole
concentration p+ layer on the electrode side.
In the light emitting diode having the above construction, each
group III nitride-based compound semiconductor layer may be formed
by MOCVD under conventional conditions, or alternatively may be
formed by a method such as a molecular beam epitaxy method (MBE
method), a halide vapor-phase epitaxy method (HVPE method),
sputtering, ion plating or electron shower.
An n-electrode 4018 has a two-layer structure of an Al layer and a
V layer. After the formation of the p-type semiconductor layer
4015, the p-type semiconductor layer 4015, the layer 4014 including
a light emitting layer, and a part of the n-type semiconductor
layer 4013 are removed by etching, and the n-electrode 4018 is
formed by vapor deposition on the n-type semiconductor layer
4013.
A p-electrode 4016 is a gold-containing film and is stacked on the
p-type semiconductor layer 4015 by vapor deposition.
After the formation of the individual semiconductor layers and
electrodes by the above steps, the step of isolating chips is
carried out.
As shown in FIG. 76A, the submount 4020 is an insulating sheet-like
member of AlN. Surface electrodes 4021, 4022 are formed on the
upper surface, and backside electrodes 4023, 4024 are formed on the
backside. These electrodes 4021, 4022, 4023, and 4024 comprise
titanium, Ni, and Au stacked in that order, and continuity is made
through a through-hole 4025 (filled with an electrically conductive
metal).
In the submount 4020 in this example, the surface electrodes 4021,
4022 are made conductive to the backside electrodes 4023, 4024
through through-holes. The continuity between these electrodes may
also be made by providing a metal layer (a side metal) on the side
face of the submount 4020.
An n-electrode in the light emitting element 4010 is electrically
connected to the surface electrode 4021 through an Au bump 4031,
and a p-electrode is electrically connected to the surface
electrode 4022 through an Au bump 4032. A solder ball may be used
instead of the bump.
A groove 4043 and a groove 4044 are formed by cutting on the edge
of the first lead frame 4041 and the edge of the second lead frame
4042 which are opposite to each other. The grooves 4043, 4044 have
such a form that both ends of the submount 4020 can be fitted
substantially without leaving any gap, whereby the position of the
submount 4020 is specified. The first and second lead frames 4041,
4042 and the submount 4020 are fixed with the aid of solder (such
as Sn--Ag-based cream solder) 4035.
In this example, the depth of the groove 4043 and the groove 4044
was regulated so that the surface of the first and second lead
frames 4041, 4042 is substantially level with the surface of the
submount 4020. This can facilitate the regulation of light
(particularly laterally released light) emitted from the light
emitting element 4010.
Further, a construction may also be adopted in which the depth of
the groove is increased to reflect light emitted from the light
emitting element 4010 by the side wall of the groove.
Thereafter, as shown in FIG. 77, the light emitting element 4010 is
covered by the sealing member 4051 to prepare a luminescent device
4050 of this example. The inclusion of a fluorescent material in
the sealing member 4051 can produce any desired luminescent color
such as white. The sealing member 4051 is properly selected from
those transparent to light emitted from the light emitting element,
for example, depending upon applications of the luminescent device.
Examples thereof include organic materials such as epoxy resins,
polyimides, and silicone elastomers and inorganic materials such as
low melting glass. In this example, the sealing member 4051 is
molded using an imide resin which can withstand reflow, followed by
soldering of the submount 4020 to the first and second lead frames
4041, 4042.
Another embodiment of the sealing member 4053 is shown in FIG. 78.
In this example, the end of the first and second lead frames 4041,
4042 and the submount 4020 are also covered by the sealing member
4053. The sealing member 4053 is formed by fixing the submount 4022
into the first and second lead frames 4041, 4042 and then
conducting molding. An epoxy resin may be adopted as the molding
material.
In the luminescent device 4050 in this example having the above
construction, heat generated in the light emitting element 4010 is
conveyed substantially evenly to the first and second lead frames
4041, 4042 through the submount 4020. Accordingly, the heat
transfer path is satisfactorily ensured to improve heat dissipation
efficiency.
The position of the submount 4020, that is, the position of the
light emitting element 4010, is specified by the groove 4043 and
the groove 4044. Therefore, stable light distribution
characteristics can be realized in the luminescent device.
Variants of each element in this example will be explained. Parts
identical to those shown in FIG. 77 and 78 are identified with the
same reference characters, and the explanation thereof will be
omitted.
In the example shown in FIG. 80, the groove 4045 in the first lead
frame 4041 is shorter, and the groove 4046 in the second lead frame
4042 is longer. According to this construction, the member
(peripheral wall of the groove 4046) of the second lead frame 4042
is located just under the light emitting element 4010. Thus, the
distance from the light emitting element 4010 to the lead frame is
the shortest, and heat can be more efficiently released from the
light emitting element 4010.
In the example shown in FIG. 80, the groove 4047 and the groove
4048 are open to the side face of the lead frames 4041, 4042. This
can further facilitate setting of the submount 4020 in the groove
4047 and the groove 4048.
In the example shown in FIG. 81, a groove 4049 was formed in the
side direction of the first lead frame 4041. As can be seen from
this example, the direction and position of formation of the groove
in the lead frame is any direction and position and may be properly
selected depending upon the applications of the luminescent
device.
In the example shown in FIG. 82, concave parts 4061, 4062 are
formed on the front end of the first and second lead frames 4041,
4042 by pressing. As with the embodiment shown in FIG. 76, a
submount can be set in the concave parts 4061, 4062.
In the example shown in FIG. 83, -shaped convexes 4071, 4072 were
formed by pressing on the front end of the first and second lead
frames 4041, 4042. The parts surrounded by the convexes 4071, 4072
constitute concaves 4073, 4074. As with the embodiment shown in
FIG. 76, a submount is set in the concave parts 4073, 4074.
FIG. 84 is a cross-sectional view showing the construction of the
luminescent device in the thirteenth embodiment. This luminescent
device 5010 includes a substrate part 5011 as a power supply
member, an LED element 5012 mounted on the upper surface of the
substrate part 5011, a buffer layer 5013 sealed so as to cover the
LED element 5012 on the upper surface of the substrate part 5011,
and a sealing member 5014 formed so as to cover the upper surface
of the buffer layer 5013 and the substrate part 5011.
The substrate part 5011 includes a ceramic substrate 5011a (an
insulating substrate) with a high expansion coefficient, wiring
layers 5011b, 5011c, 5011d and 5011e formed in a predetermined
pattern on the upper surface of the ceramic substrate 5011a, wiring
layers 5011f, 5011g formed in a predetermined pattern on the lower
surface of the ceramic substrate 5011a, an Au plating film 5011h
covered on the surface of the wiring layer 11c, an Au plating film
5011i covered on the surface of the wiring layer 5011d, an Au
plating film 5011j covered on the surface of the wiring layer
5011f, an Au plating film 5011k covered on the surface of the
wiring layer 5011g, a through-hole 5111 for connecting the wiring
layer 5011b to the wiring layer 5011f, and a through-hole 5011m for
connecting the wiring layer 5011d to the wiring layer 5011g.
The ceramic substrate 5011a may be made of, for example,
glass-containing Al.sub.2O.sub.3 material (coefficient of thermal
expansion: 13.2.times.10.sup.-6/.degree. C.). The wiring layers
5011b, 5011d, 5011j, 5011g function as electrodes for supplying
electric power. The Au plating films 5011h, 5011i, 5011j, 5011k are
provided for improving connectivity, electrical conductivity, and
corrosion resistance. In the substrate part 5011, before mounting
the LED element 5012, the wiring layers 5011b to 5011g, the Au
plating films 5011h, 5011i, 5011j, the Au plating film 5011k, and
the through-holes 5111, 5011m should be previously formed in the
ceramic substrate 5011a.
For example, the LED element 12 is made of a semiconductor such as
GaN or AlInGaP, and the chip size is, for example, 0.3.times.0.3 mm
(standard size) or 1.times.1 mm (large size). The buffer layer 5013
is made of a silicone resin. The sealing member 5014 is made of,
for example, "K-PSK100" (coefficient of thermal expansion:
11.4.times.10.sup.-6/.degree. C.) manufactured by Sumita Optical
Glass, Inc.
The sealing member 5014 is made of a glass material which is
transparent to light and has a low melting point. The LED element
5012 has on its lower surface electrodes 5012a, 5012b for power
supply, and the electrodes 5012a, 5012b are soldered onto a
predetermined wiring layer in the substrate part 11.
Assembling of the luminescent device 10 will be explained.
At the outset, the LED element 5012 is positioned so that the
electrodes 5012a, 5012b are placed on the wiring layers 5011c,
5011d in the substrate part 5011. The wiring layer 5011c is
soldered to the electrode 5012a, and the wiring layer 5011d is
soldered to the electrode 5012b.
Next, a liquid silicone resin material is dropped from just above
the center part of the LED element 5012 for coating in a layer form
on the upper surface and the whole side face of the LED element
5012 to form a buffer layer 13.
Next, in such a state that the buffer layer 5013 has been formed,
the substrate part 5011 and the LED element 5002 are placed in an
atmosphere of about 150.degree. C. to subject the buffer layer 5013
to primary curing.
Next, a sealing member 5014 made of a glass material is sealed on
the surface of the buffer layer 5013 and the surface of the
substrate part 5011. A mold is used for sealing of the sealing
member 5014, and molding into a semi-circular shape as shown in
FIG. 84 is carried out in a predetermined temperature atmosphere by
a press. Thus, the luminescent device 5010 is completed. During the
glass sealing, in the silicone resin, the chemical bond is broken
by heat to form SiO.sub.2. In this case, however, any blackening
phenomenon does not occur, and light absorption does not occur.
In the luminescent device 5010 having the above construction, for
example, when the wiring layer 5011f is located on the anode side
of the LED element 5012, a positive side of a direct current source
(not shown) is connected to the wiring layer 5011f, and a negative
side is connected to the wiring layer 5011g. When a forward voltage
is applied to the LED element 12 through the bump 2 electrically
connected to a pad electrode 5108 and an n-type electrode 5109,
carrier recombination of hole and electron occurs within the light
emitting layer in the LED element 5012 resulting in light emission.
Output light is radiated to the outside of the LED element 5012
through the sapphire substrate 5101. This light practically passes
through the sealing member 5014 and goes to the outside of the
sealing member 5014, and a part of the light is reflected from the
inner surface and goes to the outside of the sealing member
5014.
The following effects can be attained by the thirteenth
embodiment.
(1) Sealing of the whole area with the sealing member 5014 made of
a glass material can reduce light attenuation caused by yellowing
or coloring which is a problem associated with resin sealing.
(2) The provision of the buffer layer 5013 around the LED element
5012 can relax external force which is applied to the LED element
5012 through a high viscose glass material at the time of sealing
of the sealing member 5014. That is, due to the interposition of
the buffer layer 5013, the LED element 5012 does not come into
direct contact with the sealing member 5014. Therefore, stress
produced by heat expansion and heat shrinkage can be absorbed by
the buffer layer 13.
(3) Glass sealing of the LED element 5012 through the buffer layer
5013 can prevent the occurrence of cracks near the LED element
5012. The construction in which the buffer layer 5013 is provided
is particularly effective in a large (1 mm.times.1 mm) LED element
5012 in which the area of contact with the sealing member 5014 is
large.
(4) Short-circuiting between-electrodes caused by collapse of the
bump 5002 can be prevented by surrounding the LED element 5012 by
the buffer layer 5013. Further, since the buffer layer 5013 can
suppress the breaking of the bump shape, inclination of the optical
axis of the LED element 5012 by glass sealing can be prevented.
(5) When the LED element 5012 is formed by scribing a wafer, fine
concaves and convexes are formed on the side face of the scribed
LED element 5012. In the glass sealing-type luminescent device
5010, the concaves and convexes cause a stress unequal part, at the
interface of the LED element 5012 and the sealing member 5014,
which is causative of microcracking. In this case, microcracking
can be prevented upon heating shrinkage of the sealing member 5014
by providing a buffer layer 5021 on the side face as the scribing
face of the LED element 5012.
FIG. 85 is a cross-sectional view showing a variant of the
luminescent device in the thirteenth embodiment. This luminescent
device 5020 is different from the luminescent device in the
thirteenth embodiment in that the buffer layer 5021 is provided
only on the side face of the LED element 5012. This construction
also can reduce short-circuiting between-electrodes caused by
collapse of the bump 5002 and stress attributable to heat shrinkage
of the sealing member 5014. Further, since the buffer layer is not
provided on the substrate side of the LED element 12, the takeout
of light emitted from the LED element 5012 is not inhibited.
FIG. 86 is a cross-sectional view showing a luminescent device in
the fourteenth embodiment. A luminescent device 5030 shown in FIG.
86 is of a face up type and includes a substrate part 31 as a power
supply member, an LED element 5032 mounted on the upper surface of
the substrate part 31, a buffer layer 5033 sealed so as to cover
the whole LED element 5032, a sealing member 5034 formed so as to
cover the upper surface of the buffer layer 33 and the substrate
part 31, and wires 5035a, 5035b for connecting the electrode on the
LED element 5032 to the wiring layer on the substrate part
5031.
The substrate part 5031 includes a ceramic substrate 5031a as an
insulating substrate using the same material as the substrate part
5011 shown in FIG. 84, wiring layers 5031b, 5031c formed in a
predetermined pattern on the upper surface of the ceramic substrate
5031a, wiring layers 5031d, 5031e formed in a predetermined pattern
on the lower surface of the ceramic substrate 5031a, a through-hole
5031f for connecting the wiring layer 5031b to the wiring layer
5031d, and a through-hole 5031g for connecting the wiring layer
5031c to the wiring layer 5031e. An Au plating film (not shown) is
provided on the surface of the wiring layers 5031b to 5031e.
The ceramic substrate 5031a may be made of, for example, a
glass-containing Al.sub.2O.sub.3 material. The wiring layers 5031b
to 5031e function as an-electrode for supplying electric power.
Regarding the substrate part 5031, before mounting the LED element
5032, the wiring layers 5031b to 5031e and the through-holes 5031f,
5031g should be previously formed on the ceramic substrate 5031a.
The sealing member 5034 is made of a glass material which is
transparent to light and has a low melting point.
The LED element 5032 is fixed on the wiring layer 5031c with the
aid of an adhesive or the like. One electrode (not shown) on the
upper surface of the LED element 5032 is connected to the wiring
layer 5031b through a wire 5035a, and the other electrode (not
shown) on the upper surface of the LED element 5032 is connected to
the wiring layer 5031c through a wire 5035b.
The buffer layer 5033 is provided so as to cover the exposed
surface of the LED element 5032 and the wires 5035a, 5035b.
The sealing member 5034 is molded in a semispherical shape so as to
cover the surface of the buffer layer 5033, and the wiring layer
exposed on the upper surface of the substrate part 5031 and a part
of the exposed part of the substrate part 5031.
Assembling of the luminescent device 5030 will be explained.
At the outset, the substrate part 5031 comprising the wiring layers
5031b to 5031e and the through-holes 5031f, 5031g formed on the
ceramic substrate 5031a is provided. The LED element 5032 is
mounted on the wiring layer 5031c in its predetermined
position.
Next, the LED element 5032 is bonded to the wiring layers 5031b,
5031c through the wires 5035a, 5035b.
Next, a liquid silicone material is dropped to a predetermined
thickness so as to cover the exposed face of the LED element 5032
and the wires 5035a, 5035b.
The LED element 5032 and the wires 5035a, 5035b are placed in an
atmosphere of about 150.degree. C. to subject the buffer layer 5033
to primary curing. Thereafter, a sealing member 5034 is formed by
molding of a glass material around the buffer layer 5033. Thus, the
luminescent device 5030 is completed.
In this luminescent device 5030, for example, when the wiring layer
5031d is located on the anode side of the LED element 5032, a
positive side of a direct current source (not shown) is connected
to the wiring layer 5031d, and a negative side is connected to the
wiring layer 5031e. Upon energization, the LED element 5032 emits
light. This light goes out from the upper surface of the LED
element 5032 in the drawing. A major part of the light is passed
through the sealing member 5034 to the outside of the device, and
another part of the light is internally reflected within the
sealing member 5034 and then goes out to the outside of the sealing
member 5034.
In the fourteenth embodiment, the buffer layer 5033 is provided
around the LED element 5032 in the luminescent device 5030 on which
the LED element 5032 is mounted in a face up manner. Therefore, an
unfavorable phenomenon can be prevented in which, during sealing of
the glass material, the wires 5035a, 5035b are deformed or
collapsed resulting in short-circuiting between-electrodes. As with
the first embodiment, cracking near the LED element 5012
attributable to a high level of thermal expansion of the sealing
member 5034 can be prevented.
For example, when the buffer layer 5033 is not provided, setting
the temperature after glass sealing to a high value causes damage
to the LED element. Therefore, there is restriction on the
temperature, and the glass sealing is carried out in such a state
that the glass is highly viscose. As a result, the application of
external force to the wires 5035a, 5035b is unavoidable, and it is
difficult to maintain the wires 5035a, 5035b in a desired position.
For example, when the wire 5035a is collapsed by pressing of the
glass material, the wiring layers 5031b and 5031c cause short
circuiting. In this case, light emission does not occur, and, in
addition, there is an influence on the power supply side (not
shown). Incidentally, this problem does not occur in the resin
material.
In the face up-type LED element, the presence of the wire as the
metal member on the upper surface per se functions as the buffer
material. Disadvantageously, however, the wire collapses leading to
an electrical short-circuiting problem. Therefore, even when any
element like the buffer material is absent, the provision of any
electrical short circuiting preventive element through the
prevention of collapse and the like is important.
FIG. 87 is a cross-sectional view showing a luminescent device in
the fifteenth embodiment of the invention. In this luminescent
device 5040, a submount 5043 on which an LED element 5041 is
mounted is mounted on lead parts 5044a, 5044b. In FIG. 87, the
submount is shown in a non-cross-sectional state.
This luminescent device 5040 includes an LED element 5041 in which
a bump 5042 is provided on the mounting face, a submount 5043 on
which the LED element 5041 is mounted, lead parts 5044a, 5044b as a
power supply member on which the submount 5043 is mounted, a buffer
layer 5045 provided so as to cover the exposed face of the LED
element 5041, and a sealing member 5046 made of light transparent
glass to seal the buffer layer 5045 and the periphery of the buffer
layer 5045.
The submount 5043 is made of, for example, AlN (aluminum nitride)
with a high level of thermal conductivity, and the electrode 5043a
connected to the bump 5042 is formed on the mounting face side of
the LED element 5041. An electrode 5043b connected to a pair of
lead parts 5044a, 5044b is formed on the opposite side (face on the
lead frame side). A through-hole 5043c is provided within the
submount 5043 to connect the electrode 5043a to the electrode
5043b.
Lead parts 5044a, 5044b are formed as a part of the lead frame so
as to face each other while providing a predetermined gap
therebetween on the inner side of the strip part on both sides, and
a pair of lead parts are allocated to one LED element. A part of
the front end part of the lead parts 5044a, 5044b is formed in a
small thickness so as to provide a level difference, and the
submount 5043 is mounted in this level different part.
The buffer layer 5045 is provided based on the same material and
processing as the buffer layers 5013, 5021 and 5033 shown in the
above-described other embodiments.
As with the above-described other embodiments, the sealing member
5046 is made of a glass material which is transparent to light and
has a low melting point.
In this luminescent device 5040, when the lead part 5044a is a
positive (+) power supply terminal, the current supplied to the
lead part 5044a passes through the lead part 5044a, one electrode
5043b, one through-hole 5043c, one electrode 5043a, and one bump 42
and flows to the anode of the LED element 5041. The current output
from the cathode of the LED element 41 passes through the other
bump 5042, the other electrode 5043a, the other through-hole 5043c,
and the other electrode 5043b and flows to the lead part 5044b,
whereby the LED element 5041 emits light.
Assembling of the luminescent device 5040 will be explained.
At the outset, a submount 5043 on which electrodes 5043a, 5043b and
a through-hole 5043c have been previously formed is provided. An
LED element 5041 is mounted on the submount 5043 in its
predetermined position through a bump 5042, whereby the LED element
5041 is electrically connected and mechanically fixed.
Next, the LED element 5041 mounted on the submount 5043 is disposed
within a recess provided at the front end part of the lead parts
5044a, 5044b so that energization direction is identical.
Next, a liquid silicone material is dropped to a predetermined
thickness so as to cover the periphery of the LED element 5041.
The LED element 5032, the submount 5043, and the lead parts 5044a,
5044b are placed in an atmosphere of about 150.degree. C. to
perform primary curing, thereby forming the buffer layer 5045
around the LED element 5032.
The glass sheet for forming the sealing member 5045 is disposed on
and under the LED element 5041. Further, a mold is disposed on the
upper side and lower side of the LED element 5041.
Next, a glass sheet is molded into a predetermined form by pressing
using the molds in an atmosphere of a predetermined temperature.
Thus, a luminescent device 5040 is completed. Finally, the other
end of the lead parts 5044a, 5044b is separated from the lead frame
for isolation into individual luminescent devices 5040.
In the fifteenth embodiment, in sealing the LED element 5041
mounted on the submount 5043 with a high level of thermal
conductivity by a glass material, the buffer layer 5045 can prevent
cracking or separation around the LED element 5041 and the submount
5043 due to a difference in coefficient of thermal expansion.
In the luminescent device 5040, a phosphor may be mixed in the
buffer layer 5045. In this case, wavelength conversion takes place
based on mixing of excitation light emitted from the phosphor
excited by light emitted from the LED element 5041 with light
emitted from the LED element 5041. For example, Ce (cerium):YAG
(yttrium aluminum garnet), which is excited by blue light emitted
from the LED element 5041 and emits yellow light, may be mentioned
as the phosphor.
FIG. 88 is a cross-sectional view showing a luminescent device in
the sixteenth embodiment of the invention. This luminescent device
5050 has a construction comprising a heat dissipating member
mounted on the luminescent device 5040 shown in FIG. 87. That is,
this luminescent device is characterized in that a heat dissipating
member 5051 using a metallic material having a high level of
thermal conductivity such as copper is mounted on the lower part of
the submount 5052 such as AlN.
The luminescent device 5050 includes a heat dissipating member 5051
which, functions as a radiator, a submount 5052 mounted on the heat
dissipating member 5051, lead parts 5053a, 5053b of which the front
end is mounted on a level difference part on both ends of the
submount 5052, an LED element 5041, which has a pair of bumps 5042
for power supply on its lower surface and is mounted on the
submount 5052, a buffer layer 5054 provided so as to cover the
exposed face of the LED element 5041, and a sealing member 5055
made of low-melting transparent glass for sealing the buffer layer
5054 and the periphery of the buffer layer 5054.
The submount 5052 is worked in a small thickness so as to cause a
level difference in a predetermined range on both ends, and the
front end of the lead parts 5053a, 5053b is mounted on the small
thickness part. The front end is connected to the side face of the
wiring patterns 5052a, 5052b by soldering or the like. Further,
wiring patterns 5052a, 5052b in contact with a pair of bumps 5042
are provided on the submount 5052 from the upper surface toward the
side face.
The buffer layer 5054 has stress buffering and wavelength
conversion function imparted by mixing a phosphor in a Si-based
alkoxide and sintering the mixture to form a phosphor-containing
SiO.sub.2 in a porous state as the buffer layer.
As explained in the fifteenth embodiment, Ce (cerium):YAG (yttrium
aluminum garnet) and the like may be used as the phosphor.
The luminescent device 5050 in the sixteenth embodiment may be
assembled as explained in the fifteenth embodiment, and, thus,
overlapped explanation thereof will be omitted. That is, after the
part above the submount 5052 in FIG. 88 is completed, the heat
dissipating member 5051 may be mounted on the lower face with the
aid of an adhesive.
The following effects can be attained by the sixteenth
embodiment.
(1) Since the heat dissipating member 5051 for promoting heat
dissipation is provided on the lower part of the submount 5052,
heat generated upon lighting of the LED element 5041 can be
efficiently diffused to the outside of the device, and the
occurrence of thermal expansion and thermal shrinkage upon a
temperature rise of the sealing member 5055 made of a glass
material and the like can be suppressed to prevent the occurrence
of cracking.
(2) Mixing the phosphor in the buffer layer 5054 can realize
wavelength conversion and, at the same time, can improve light
takeout efficiency.
In the above embodiments, a reflecting surface may be formed on the
surface of the substrate parts 5011, 5031 and the lead parts 5044a,
5044b, 5053a, 5053b to enhance light outgoing efficiency.
A method may also be adopted in which a phosphor is mixed in a part
of the LED elements 5012, 5032 within the sealing members 5014,
5034, that is, in the upper part of the LED elements 5012, 5032, or
a phosphor for wavelength conversion may be mixed in the buffer
layers 5013, 5033.
When the buffer layer 5054 is made of a TiO.sub.2-based ceramic
material, the refractive index is as high as 2.4. Therefore,
efficiency of takeout of light from the LED element 5041 can be
enhanced.
In the above embodiments, one LED element was provided within one
sealing member. Alternatively, however, two or more LED elements
may be provided to constitute a multi-emission-type luminescent
device. In this case, a plurality of LED elements to be mounted may
be different from each other in emission color, or alternatively
the plurality of LED elements may be identical to each other in
emission color. Further, regarding the drive mode of the LED
elements, all of the plurality of LED elements may be connected in
parallel, or alternatively a plurality of LED element groups may be
connected in parallel. Further, a plurality of LED elements may be
connected in series, or alternatively all the LED elements may be
connected in series.
Further, "K-PSK100" manufactured by Sumita Optical Glass, Inc. was
used as the sealing member 5014. The sealing member, however, is
not limited to this only and may be other glass so far as the glass
can be softened at such a temperature that can realize sealing
without causing thermal damage to the light emitting element.
In the above embodiments, the form of the sealing members 5014,
5034, 5046, 5055 is semispherical. The invention, however, is not
limited to the form shown in the drawings, and any form such as a
form not having any lens part, a polygonal form, or a cylindrical
form may be adopted.
Further, in molding the sealing members 5014, 5034, 5046, 5055, the
molding method is not limited to pressing using a glass sheet.
Other sealing methods, for example, a method in which fused glass
is fed to a portion near the LED element and heat molding is
carried out in a mold may be adopted.
Further, the buffer layer 5054 is not always required to be porous
and may be any layer so far as it has cushioning effect, insulating
properties and heat resistance, for example, it is brittle and
absorbs stress, and the coefficient of thermal expansion is
intermediate between that of the LED element and that of the
sealing glass.
FIG. 89 is a cross-sectional view showing the construction of the
luminescent device in the seventeenth embodiment of the invention.
This luminescent device 6010 includes a substrate part 6011 as a
power supply member, an LED element 6012 which has at least a pair
of bumps 6012a, 6012b for power supply made of Au and is mounted on
the upper surface of the substrate part 6011, an insulating layer
6013 filled into between the lower face of the LED element 6012 and
the substrate part 6011, and a sealing member 6014 formed so as to
cover the LED element 6012 and the upper surface of the substrate
part 6011.
The substrate part 6011 includes a ceramic substrate 6011a, wiring
layers 6011b, 6011c, 6011d and 6011e formed in a predetermined
pattern on the upper surface of the ceramic substrate 6011a, wiring
layers 6011f, 6011g formed in a predetermined pattern on the lower
surface of the ceramic substrate 6011a, an Au plating film 6011h
covered on the surface of the wiring layer 6011c, an Au plating
film 6011i covered on the surface of the wiring layer 6011d, an Au
plating film 6011j covered on the surface of the wiring layer
6011f, an Au plating film 6011k coated on the surface of the wiring
layer 6011g, a through-hole 6111 for connecting the wiring layer
6011b to the wiring layer 6011f, and a through-hole 6011m for
connecting the wiring layer 6011d to the wiring layer 6011g.
The ceramic substrate 6011a may be made of, for example,
glass-containing Al.sub.2O.sub.3 material (coefficient of thermal
expansion: 13.2.times.10.sup.-6/.degree. C.). The wiring layers
6011c, 6011d, 6011f, 6011g function as electrodes for supplying
electric power. The Au plating films 6011h, 6011i, 6011j, 6011k are
provided for improving connectivity, electrical conductivity, and
corrosion resistance. In the substrate part 6011, before mounting
the LED element 6012, the wiring layers 6011b to 6011g, the Au
plating films 6011h, 6011i, 6011j, the Au plating film 6011k, and
the through-holes 6011l, 6011m are previously formed in the ceramic
substrate 6011a.
For example, the LED element 6012 is made of a semiconductor such
as GaN or AlInGaP, and the chip size is, for example, 0.3.times.0.3
mm (standard size) or 1.times.1 mm (large size). The LED element
6012 has on its lower surface electrodes 6012a, 6012b for power
supply, and the electrodes 6012a, 6012b are soldered to a
predetermined wiring layer in the substrate part 6011.
The insulating layer 6013 is made of a silicone material, or
diamond, BN, SiC or AlN power containing insulating material. When
a silicone resin is used as the silicone material, upon exposure to
a high temperature involved in sealing of the sealing member 6014,
the chemical bond is cleaved to form SiO.sub.2 which functions as a
heat resistant insulator. Instead of SiO.sub.2 formed from the
silicone resin, ceramics formed from Si-based, Ti-based or other
alkoxides may also be used. The diamond has a high level of thermal
conductivity. BN, SiC, and AlN are inferior to diamond in thermal
conductivity but are more inexpensive. Diamond, BN, and SiC are
transparent or white and have a feature of low light
absorption.
The sealing member 6014 is made of a glass material which is
transparent to light and has a low melting point, and, for example,
"K-PSK100" manufactured by Sumita Optical Glass, Inc. (coefficient
of thermal expansion: 11.4.times.10.sup.-6/.degree. C.) may be
used. According to an experiment conducted by the inventors, in
order to provide good bonding between ceramic and glass, the
ceramic substrate 6011a and the sealing member 6014 should be
substantially identical to each other in coefficient of thermal
expansion (the thermal expansion coefficient difference ratio being
within 15%), and, in this case, the thermal expansion coefficient
ratio is 0.86.
Assembling of the luminescent device 6010 will be explained.
Positioning is carried out so that bumps 6012a, 6012b of Au are put
on the wiring layers 6011c, 6011d. The LED element 6012 is provided
on the substrate part 6011, and the insulating layer 13 is then
formed, for example, by dropping or filling.
Next, the LED element 6012, the exposed area of the insulating
layer 6013, and the exposed area of the substrate part 6011 are
sealed with the sealing member 6014 by the glass material. A mold
is used for sealing of the sealing member 6014, and molding into a
semicircular form as shown in FIG. 89 is carried out at a
predetermined temperature atmosphere by pressing. In this sealing,
the silicone material as the insulating layer 6013 is converted to
SiO.sub.2, and the lower surface of the LED element 6012 and the
bumps 6012a, 6012b are fixed. Therefore, for example, the
deformation of bumps 6012a, 6012b and short-circuiting between
bumps can be avoided. Thus, the luminescent device 6010 is
completed.
In this luminescent device 6010, for example, when the wiring layer
6011f is located on the anode side of the LED element 6012, a
positive side of a direct current source (not shown) is connected
to the wiring layer 6011f, and a negative side is connected to the
wiring layer 6011g. When a forward voltage is applied to the LED
element 6012 through the bump 6002 electrically connected to a
p-type electrode and an n-type electrode (not shown), in the active
layer of the LED element 6012, carrier recombination of hole and
electron occurs, resulting in light emission. Output light is
radiated to the outside of the LED element 6012. This light
practically passes through the sealing member 6014 and goes to the
outside of the sealing member 6014, and a part of the light is
reflected from the inner surface and goes to the outside of the
sealing member 6014.
The following effects can be attained by the seventeenth
embodiment.
(1) Sealing of the whole area with the sealing member 6014 made of
a glass material can reduce light attenuation caused by yellowing
or coloring which is a problem associated with resin sealing.
(2) By virtue of the provision of the heat resistant insulating
layer 13 on the lower side of the LED element 6012, during sealing
of the sealing member 14, an unfavorable phenomenon can be
prevented in which the sealing member 6014 presses in a high
temperature state the bumps 6012a, 6012b to damage the LED element
6012. That is, deformation or breaking of bumps 6012a, 6012b under
high temperature and high pressure conditions of the sealing member
14 which causes short-circuiting between bumps can be
prevented.
(3) When a diamond, BN, SiC or AlN powder-containing insulating
material is used, the effect of dissipating heat generated from the
LED element 6012 can be expected. Therefore, heat dissipating
properties can be improved.
FIG. 90 is a cross-sectional view showing the construction of a
luminescent device in the eighteenth embodiment. This luminescent
device 6020 is of a metal lead type in which a light emitting
element is mounted on a lead frame using a submount 6022. The
luminescent device 6020 includes an LED element 6021 in which bumps
6021a, 6021b are provided on the mounting face, a submount 6022 on
which this LED element 6021 is mounted, lead parts 6023a, 6023b as
a power supply member on which the submount 6022 is mounted, an
insulating layer 6024 filled into between the upper surface of lead
parts 6023a, 6023b and the lower surface of the LED element 6021,
and a sealing member 6025 made of a light transparent glass for
sealing the end of the insulating layer 6024 and the front end of
the lead parts 6023a, 6023b including the surface of the LED
element 6021.
The submount 6022 is made of, for example, AlN (aluminum nitride)
with a high level of heat conductivity. A wiring layer 6022a
connected to one bump 6021a is provided on the upper face, side
face, and lower face so as to provide a -shaped form, and, on the
opposite side, the wiring layer 6022b connected to the bump 6021b
is provided on the upper face, side face, and lower face so as to
provide a -shaped form.
If necessary, the submount 6022 may incorporate a circuit such as a
Zener diode for element destruction preventive purposes. Further,
instead of the wiring layers 6022a, 6022b, wiring means comprising
a combination of electrodes provided on the upper and lower faces
with a through-hole for communication of the upper and lower
electrodes with each other may be used.
The lead parts 6023a, 6023b are made of a copper-based or
iron-based metal and are provided so as to face each other while
providing a predetermined space therebetween on the inner side of
the strip part on both sides as a part of a lead frame (not shown),
and a pair of lead parts are provided for each one LED element. A
part of the front end of the lead parts 6023a, 6023b is formed in a
small thickness so as to form a level difference, and a submount
6022 is mounted in this level difference part.
As with the insulating layer 6013 in the seventeenth embodiment,
the insulating layer 6024 may be made of a silicone material, or a
diamond or AlN powder-containing insulating material. For example,
the process of conversion of the silicone material to SiO.sub.2 by
cleaving of the chemical bond upon sealing of the sealing member
6025, and the heat dissipating effect attained by using a diamond,
BN, SiC, or AlN powder-containing insulating material are the same
as those in the case of the insulating layer 6013.
As with the above embodiments, the sealing member 6025 is made of a
glass material which is transparent to light and has a low melting
point.
In this luminescent device 6020, when the lead part 6023a is a
positive (+) power supply terminal, current supplied to the lead
part 6023a is passed through the lead part 6023a, the wiring layer
6022a, and the bump 6021a and flows to the anode of the LED element
6021. Further, the current output from the cathode of the LED
element 21 is passed through the bump 6021b and the wiring layer
6022b and flows to the lead part 6023b, whereby the LED element
6021 emits light.
Assembling of the luminescent device 6020 will be explained.
At the outset, a submount 6022 with wiring layers 6022a, 6022b
previously formed thereon is provided. Bumps 6021a, 6021b are
formed at predetermined positions on the submount 6022. The LED
element 6021 is mounted thereon. The bump 6021a and bump 6021b are
connected to the wiring layer 6022a and the wiring layer 6022b,
respectively, for electrical connection and mechanical
fixation.
Next, the LED element 6021 mounted on the submount 6022 is disposed
within the recess at the front end of the lead parts 6023a, 6023b
so that the energization direction is made identical.
Alternatively, after the LED element 21 is mounted on the submount
6022, the submount 6022 may be mounted on the lead parts 6023a,
6023b.
Next, a silicone material as the insulating layer 6024 is filled
into between the lower face of the LED element 6021 and the upper
face of the submount 6022 (this filling may be carried out before
mounting the submount 22 on the lead parts 6023a, 6023b). In this
state, the assembly is carried in the mold. A glass sheet (not
shown) for the formation of the sealing member 25 is disposed on
and under the LED element 6021, and molding into a semispherical
shape is carried out at a predetermined temperature by pressing. In
this sealing, the silicone material is converted to SiO.sub.2 to
form an insulating layer 6024 which fixes the lower face of the LED
element 6021 and the bumps 6012a, 6012b. Therefore, for example,
the deformation of bumps 6012a, 6012b and short-circuiting between
bumps can be avoided. Thus, the luminescent device 6020 is
completed. Finally, the other end of the lead parts 6023a, 6023b is
isolated from a lead frame (not shown) into individual luminescent
devices 6020.
In the eighteenth embodiment, the use of lead parts 6023a, 6023b
having excellent adhesion to the glass material and the provision
of the insulating layer 6024 on the lower side of the LED element
6021 can avoid damage to the LED element 6021 by the sealing member
6025 at the time of sealing of the sealing member 6025, and, thus,
deformation, movement, short-circuiting or the like in the bumps
6021a, 6021b can be prevented. Further, sealing of the whole
assembly with the sealing member 6025 made of a glass material can
prevent light attenuation caused by yellowing or coloration as in
the case where the sealing member is made of a resin material.
FIG. 91 is a cross-sectional view showing a luminescent device in
the nineteenth embodiment. As with the eighteenth embodiment, this
luminescent device 6030 is of a metal lead type in which a light
emitting element is mounted on a lead frame using a submount. Here
as with FIG. 90, only the construction of the principal part is
shown, and, further, a submount 6032 is shown in a non-cross
sectional state. This embodiment is different from the eighteenth
embodiment in the structure of the submount and the construction
and formation area of the insulating layer.
This luminescent device 30 includes an LED element 6031 provided
with bumps 6031a, 6031b on its mounting face, a submount 6032 on
which the LED element 6031 is mounted, lead parts 6033a, 6033b as a
power supply member in which the submount 6032 is mounted at the
front end thereof, an insulating layer 6034 in which a phosphor
6034a has been mixed and which is formed by filling or dropping so
as to cover the whole area of the LED element 6031, and a sealing
member 6035 made of a light transparent glass for sealing the front
end of the lead parts 6033a, 6033b including the upper face of the
LED element 6031.
The submount 6032 is made of, for example, AlN (aluminum nitride)
with a high level of thermal conductivity, and electrodes 6032a,
6032b connected to the bumps 6031a, 6031b are formed on the
mounting face side of the LED element 6031. Electrodes 6032c, 6032d
connected to a pair of lead parts 6033a, 6033b are formed on the
opposite face (lead frame side). Through-holes 6032e, 6032f are
provided within the submount 6032 for connection of the electrode
6032a to the electrode 6032c and connection of the electrode 6032c
to the electrode 6032d.
The lead parts 6033a, 6033b are made of a copper-based or
iron-based metal and are provided so as to face each other while
providing a predetermined space therebetween on the inner side of
the strip part on both sides as a part of a lead frame (not shown),
and a pair of lead parts are provided for each one LED element. A
part of the front end of the lead parts 6033a, 6033b is formed in a
small thickness so as to form a level difference, and a submount
6032 is mounted in this level difference part.
The insulating layer 6034 is composed mainly of a silicone
material, and a phosphor 6034a is mixed in the silicone material.
The formation process of SiO.sub.2 by cleaving of the chemical bond
of the silicone material upon sealing of the sealing member 6025,
and, for example, the heat dissipating effect attained by using a
diamond or AlN powder-containing insulating material are the same
as those in the case of the insulating layer 6013.
For example, when the LED element 6021 is a blue light emitting
element, Ce (cerium):YAG (yttrium aluminum garnet), which is
excited by blue light emitted from the LED element and emits yellow
light, is used as the phosphor 6034a.
As with the above embodiments, the sealing member 6035 is made of a
glass material which is transparent to light and has a low melting
point.
In this luminescent device 6030, when the lead part 6033a is a
positive (+) power supply terminal, current supplied to the lead
part 6033a is passed through the lead part 6033a, the electrode
6032c, the through-hole 6032e, the electrode 6032a, and the bump
6031a and flows to the anode of the LED element 6031. Further, the
current output from the cathode of the LED element 6031 is passed
through the bump 6031b, the electrode 6032b, the through-hole
6032f, and the electrode 6032d and flows to the lead part 6033b,
whereby the LED element 6031 emits light.
Assembling of the luminescent device 6030 will be explained.
At the outset, a submount 6032 with electrodes 6032a to 6032d and
through-holes 6032e, 6032f previously formed thereon is provided.
Bumps 6031a, 6031b are formed at predetermined positions on the
submount 6032. The LED element 6031 is mounted thereon, whereby the
LED element 6031 is electrically connected to the electrodes 6032a,
6032b through the bumps 6031a, 6031b and, at the same time, is
mechanically fixed.
Next, the LED element 6031 mounted on the submount 6032 is disposed
within the recess at the front end of the lead parts 6033a, 6033b
so that the energization direction is made identical.
Alternatively, after the submount 6032 is mounted on the lead parts
6033a, 6033b, the LED element 6031 may be mounted on the submount
6032.
Next, an insulating layer 6034 with a phosphor 6034a mixed therein
is formed so as to extend to the upper face, side face, and upper
face of the submount 6032 by dropping or filling.
The assembly is carried in the mold. A glass sheet (not shown) for
the formation of the sealing member 35 is disposed on and under the
LED element 6031, and molding into a semispherical shape is carried
out at a predetermined temperature by pressing. Thus, the
luminescent device 6030 is completed. In this sealing, the silicone
material is converted to SiO.sub.2 to form an insulating layer 6034
which fixes the lower face of the LED element 6031 and the bumps
6031a, 6031b. Therefore, for example, the deformation of bump 6012a
and short-circuiting between bumps can be avoided. Finally, the
other end of the lead parts 6033a, 6033b is isolated from a lead
frame into individual luminescent devices.
The following effects are attained by the nineteenth
embodiment.
(1) The provision of the insulating layer 6034 can avoid damage to
the LED element 6031 by the sealing member 6035 at the time of
sealing of the sealing member 6035, and, thus, deformation,
movement, short-circuiting or the like in the bumps 6031a, 6031b
can be prevented.
(2) Since the phosphor 6034a is mixed in the insulating layer 6034,
light absorption by the electrode on the lead part (or the wiring
layer on the submount) can be reduced. In general, Au plating is
provided on the electrode and the wiring layer. This Au plating has
a high level of blue or purple light absorption. The provision of
the phosphor-mixed insulating layer 6034, however, can realize
wavelength conversion of light emitted from the side face of the
LED element to prevent light absorption on the Au plating face.
(3) Wavelength conversion is also possible for light emitted from
the upper face of the LED element 6031.
Further, since the whole assembly is sealed with the sealing member
6035 made of a glass material, light attenuation caused by
yellowing or coloring, which is a problem in the case where the
sealing member is a resin material, can be prevented.
Instead of the submount 6032, a submount 6022 having ""-shaped
wiring layers 6022a, 6022b shown in FIG. 90 may be used. Contrary
to this, instead of the submount 6022 shown in FIG. 90, the
submount 6032 shown in FIG. 91 may be used.
FIG. 92 is a plan view showing the bump forming face of an LED
element of a standard size. This LED element 6031 is an LED element
having a size of 0.3 mm square and includes a small pattern 6042
with a bump 6041 connected to an n-electrode mounted thereon, a
large pattern 6043 connected to a p-electrode, and bumps 6044a,
6044b mounted on this large pattern 6043. The higher the output of
the LED element 6031 is, the larger the current is. Accordingly,
plural bumps are provided on the p-electrode side so as to cope
with a large current capacity.
FIG. 93 is a plan view showing the bump forming face of the
large-size LED element. This LED element 6031 is an LED element
having a size of 1 mm square and includes a wiring pattern 6054 on
which bumps 6052a, 6052b are provided, and a wiring pattern 6055 on
which bumps 6053a to 6053p are provided. Since the large-size LED
element has a larger emission area than the standard size, larger
current flows. Accordingly, in order to have uniform light emission
on the light emitting face, depending upon the form, area of the
wiring patterns 6054, 6055, for each wiring pattern, plural bumps
are provided as electrode contacts.
As shown in FIGS. 92 and 93, in the LED element for electrical
connection through bumps, the bumps are likely to collapse upon
exposure to temperature and pressure at the time of glass sealing.
In particular, as shown in FIG. 93, when a number of bumps 6053a to
6053p are provided, the distance between bumps is so small that
deformation of bumps is more likely to cause short-circuiting. In
this LED element 6031, the insulating layer 6034 covers the bump
forming face to ensure insulation between the bumps and can
withstand the pressure applied at the time of glass sealing to
suppress the deformation of bumps 6053a to 6053p. As a result, the
sealing member 6035 made of a glass material can be formed.
In the above embodiments, the bumps 6012a, 6012b are made of Au.
The material for the bumps, however, is not limited to Au, and
bumps formed by soldering may be used. Further, instead of bumps,
solder plating formed in-electrodes may be used. When "K-PSK100"
manufactured by Sumita Optical Glass, Inc. is used, sealing is
carried out at a temperature above 400.degree. C. and the viscosity
of glass during processing is so high that even Au bumps collapse.
On the other hand, in the case of a hybrid low-melting glass as an
inorganic-organic mixture, sealing at a lower temperature is
possible. As in solder bumps, when the melting point is below the
sealing temperature, short-circuiting between-electrodes occurs
even at a lower pressure. This invention is effective to overcome
this problem.
Further, in the above embodiments, a phosphor layer for wavelength
conversion may be formed on the upper part of the LED elements
6012, 6032 within the sealing members 6014, 6025, 6035.
Furthermore, in the above embodiments, one LED element was provided
within one sealing member. Alternatively, however, two or more LED
elements may be provided to constitute a multi-emission-type
luminescent device. In this case, a plurality of LED elements to be
mounted may be different from each other in emission color, or
alternatively the plurality of LED elements may be identical to
each other in emission color. Further, regarding the drive mode of
the LED elements, all of the plurality of LED elements may be
connected in parallel, or alternatively a plurality of LED element
groups may be connected in parallel. Further, a plurality of LED
elements may be connected in series, or alternatively all the LED
elements may be connected in series.
In the above embodiments, the sealing members 6014, 6025, 6035 are
in a dome form. The invention, however, is not limited to the form
shown in the drawings, and any form such as a form not having any
lens part, a polygonal form, or a cylindrical form may be
adopted.
Further, the method for molding the sealing members 6014, 6025,
6035 is not limited to the molding method using a glass sheet by
pressing, and other sealing methods may also be used.
FIG. 94 is a cross-sectional view showing the construction of a
luminescent device in the twentieth embodiment of the invention. In
general, the lead frame is provided with a strip (not shown) to
both sides of which the outer side of each lead part is connected.
In general, plural LED elements are mounted on the lead frame. Here
only one of the plural LED elements is shown. Further, in FIG. 94,
the submount is shown in a non-cross sectional state.
The luminescent device 7010 is of a metal lead mounting type and
includes a GaN-based LED element 7001 (coefficient of thermal
expansion: 4.5 to 6.times.10.sup.-6/.degree. C.) which is subjected
to flip chip bonding through a bump 7002 onto the mounting face, a
submount 7003 on which the LED element 7001 is mounted, lead parts
of Cu (coefficient of thermal expansion 15 to
17.times.10.sup.-6/.degree. C., thermal conductivity 400
Wm.sup.-1k.sup.-1) 7004A, 7004B as a power supply member on which
the submount 3 is mounted, and a sealing member 7005 made of
transparent glass for sealing the LED element 7001 and the
periphery around the LED element 7001.
The submount 7003 is made of, for example, AlN (aluminum nitride:
coefficient of thermal expansion 5.times.10.sup.-6/.degree. C.,
thermal conductivity 180 Wm.sup.-1k.sup.-1). Electrodes 7031A,
7031B connected to the bump 7002 are formed on the mounting face
side of the LED element 1, and electrodes 7032A, 7032B for
connection to a pair of lead parts 7004A, 7004B are formed on the
opposite face (lead frame side face). The level of the mounting
face of the LED element 7001 on the upper face of the lead parts
7004A, 7004B is lower by one step than the other part, and the
submount 7003 is disposed within this recess. A through-hole 7033
is provided within the submount 7003 for connection of the
electrodes 7031A, 7031B to the electrodes 7032A, 7032B.
The sealing member 7005 is formed by heat fusing a glass sheet,
which is transparent and has a low melting point and a coefficient
of thermal expansion close to the lead parts 7004A, 7004B (or
within a predetermined difference in coefficient of thermal
expansion), and constitutes a light transparent glass part for
sealing the LED element 7001, the submount 7003, and a part of the
lead parts 7004A, 7004B.
When the lead part 7004A is a positive (+) power supply terminal,
current supplied to the lead part 7004 is passed through a lead
part 7004A, one of electrodes 7032A, 7032B, one via hole 7033, one
of electrodes 7031A, 7031B, and one bump 7002 and flows to the
anode of the LED element 7001. Further, the current output from the
cathode of the LED element 7001 is passed through the other bump
7002, the other one of the electrodes 7031A, 7031B, the other via
hole 7033, and the other one of the electrodes 7032A, 7032B and
flows to the lead part 704B, whereby the LED element 7001 emits
light.
FIG. 95 is a plan view showing such a state that a submount has
been mounted on a lead frame. The LED element 7001 is mounted at
the center part of the submount 7003. The lead parts 7004A, 7004B
are formed as a part of the lead frame so as to face each other
while providing a predetermined gap therebetween on the inner side
of the strip part on both sides, and a pair of lead parts are
allocated to one LED element.
FIG. 96 is a diagram showing a state just before glass sealing
using a mold and is a diagram taken on line A-A of FIG. 95. The
method for the manufacture of the luminescent device 7010 will be
explained in conjunction with FIGS. 94 to 96.
The LED element 7001 provided with bumps 7002 is positioned on the
submount 7003, followed by reflow for electrical connection of the
bumps 7002 to the electrodes 7031 and mechanical fixation.
Next, the LED element 7001 mounted on the submount 7003 is disposed
within a recess provided at the front end of the lead parts 7004A,
7004B so that energization direction is identical. A submount in
which electrodes 7031A, 7031B, electrodes 7032A, 7032B and via
holes 7033 have been previously formed is used as the submount
7003.
Next, a lead frame 7006 is carried in a mold, and glass sheets
7007, 7008 are disposed respectively on and under the LED element
7001. The glass sheets 7007, 7008 are for sealing member 7005
formation and has such a size that a plurality of LED elements 7001
are simultaneously sealed.
Next, an upper mold 7011 is disposed so as to cover the glass sheet
7007. Further, a lower mold 7012 is disposed so as to cover the
glass sheet 7008. The glass sheets 7007, 7008 are then heated at
450.degree. C. in a vacuum atmosphere for softening, and, in this
state, the upper mold 7011 and the lower mold 7012 are moved in a
direction indicated by an arrow shown in FIG. 95 to apply pressure
to the glass sheets 7007, 7008. As a result, the glass sheets 7007,
7008 are molded into a dome like the sealing member 7005 shown in
FIG. 94 along the upper mold 7011 in its concave part 7011A and the
lower mold 7012 in its concave part 7012A.
Next, unnecessary parts such as the strip part in the lead frame
7004 are removed to isolate individual luminescent devices 7010
from the lead frame 7004.
In the luminescent device 7010, when a forward voltage is applied
through the bump 7002 electrically connected to the pad electrode
7108 and the n-type electrode 7109, carrier recombination of hole
and electron occurs within the active layer in the LED element 7001
resulting in light emission. The output light is emitted through
the sapphire substrate 7101 to the outside of the LED element 7001.
This output light is then radiated to the outside of the device
through the sealing member 7005.
The following effects can be attained by the twentieth
embodiment.
(1) Since the whole LED element 7001 having a lower coefficient of
thermal expansion has been sealed with and surrounded by the
sealing material 7005 made of a glass material having a larger
coefficient of thermal expansion, the internal stress produced
based on a difference in coefficient of thermal expansion is
regulated so as to be directed to the center of the LED element
7001. That is, even when internal stress based on heat shrinkage of
the glass material occurs after glass sealing, the internal stress
functions as compressive force directed to the center direction of
the LED element 1. Therefore, the glass material having strength
against the compression can realize glass sealing structure without
breaking.
(2) The LED element 7001 having a lower coefficient of thermal
expansion is mounted on the submount 7003 having a lower
coefficient of thermal expansion, and the assembly is mounted on
the lead parts 7004A, 7004B having a higher coefficient of thermal
expansion. Accordingly, for the glass material constituting the
sealing member 7005, the adhesion to both the LED element 7001
having a lower coefficient of thermal expansion and the lead parts
7004A, 7004B having a higher coefficient of thermal expansion are
required. In this case, a glass material having a coefficient of
thermal expansion close to that of the LED element 7001 is
preferably selected for sealing. The lead parts 7004A, 7004B made
of a soft metal such as Cu is more elastic than the glass material.
Therefore, if the difference in coefficient of thermal expansion
between the lead parts, and the LED element 1 and the submount 3 is
in the range of 150% to 400%, then the stress based on the heat
shrinkage difference can be structurally absorbed while maintaining
good adhesion to the glass material. This indicates that cracking
or other unfavorable phenomenon does not occur even in the case
where the lead parts 7004A, 7004B are sandwiched by the glass
material for sealing.
(3) Even in the case where the electric power applied to the LED
element 7001 is so large that the temperature of the generated heat
is increased due to the electric power, the heat generated from the
LED element 7001 can be released to the outside of the device,
whereby a lowering in emission efficiency can be effectively
prevented. In particular, this can be realized by bringing the
thermal conductivity of the submount 7003 and the lead parts 7004A,
7004B to not less than 100 Wm.sup.-1k.sup.-1.
(4) Since the sealing member 7005 is formed using the low melting
glass sheets 7007, 7008, the time necessary for heating can be
shortened and, in addition, the use of a simple heating device
becomes possible. This can facilitate glass sealing.
(5) A failure such as cracking is less likely to occur during
processing. Therefore, a high level of glass sealing properties can
be stably maintained for a long period of time, there is no
deterioration in luminescence characteristics even in water and
under highly humid conditions, and, thus, excellent durability can
be realized for a long period of time.
In the first embodiment, a construction using a GaN-based LED
element 7001 as the LED element 7001 has been explained. However,
it should be noted that the LED element is not limited to the
GaN-based LED element and other LED elements may also be used.
Further, in the above embodiments, a construction in which the
submount 7003 made of AlN is mounted on the lead parts 7004A, 7004B
made of Cu has been explained. Alternatively, for example, a
construction may also be adopted in which a submount 3 made of Si
(coefficient of thermal expansion 170 Wm.sup.-1k.sup.-1) is mounted
on a lead part made of brass (coefficient of thermal expansion 106
Wm.sup.-1k.sup.-1).
Further, the method for the formation of the sealing member 7005 is
not limited to one in which plural LED elements 7001 and submounts
7003 are sealed at a time with a glass sheet, and a method may also
be adopted in which a melted glass material is fed to a part around
the LED element 7001 and the submount 7003 followed by heat
pressing using an upper mold 7011 and a lower mold 7012 to form the
sealing member. Further, the glass material used is also not
limited to a transparent glass material and may be a colored glass
material so far as the glass material is transparent to light.
Further, the sealing member 7005 may be in various forms depending
upon specifications or the like. Examples of forms usable herein
include round, elliptical, or quadrilateral forms and, further,
forms with or without a lens.
In the above twentieth embodiment, the flip chip-type luminescent
device using a metal lead as a power supply member has been
explained. However, it should be noted that application to other
types of luminescent devices is possible. For example, application
to a face up (FU)-type luminescent devices using wire bonding is
possible.
FIG. 97 is a cross-sectional view showing a variant of the
luminescent device in the twentieth embodiment. The construction of
this luminescent device 7010 is that, in order to prevent cracking
caused by heat expansion and heat shrinkage of the sealing member
7005, an inclined part 7003A is provided by removing a corner part
of the submount 7003. The use of this submount 3 can realize a
glass sealing luminescent device 7010 which, in addition to
advantageous effects attained by the twentieth embodiment, is
advantageously less likely to cause cracking.
FIG. 98 is a cross-sectional view showing a face up-type
luminescent device in the twenty-first embodiment of the invention.
This luminescent device 7040 includes lead parts 7004A, 7004B as a
power supply member disposed horizontally on a straight line at the
front end while providing a space therebetween, a GaN-based LED
element 7041 mounted on the upper face of the front end of the lead
part 7004A through an adhesive or the like, a wire 7042 for
connecting two electrodes (not shown) on the LED element 7041 to
the lead parts 7004A, 7004B, and a sealing member 7005 made of a
glass material for sealing LED element 7041 and the front end part
of the lead parts 7004A, 7004B.
The sealing member 7005 is made of a glass material which is
transparent, has a low melting point, and has a coefficient of
thermal expansion in a predetermined value range. In particular, in
the face up type, when a wire is used, in the glass sealing, the
heat softened wire 7042 and wire connection 7042A are likely to be
collapsed upon exposure to pressure, and, consequently, for
example, short-circuiting is likely to occur. For this reason, the
use of a glass material having the lowest possible melting point is
preferred.
Assembling of the luminescent device 7040 will be explained.
At the outset, in such a state before the separation of the lead
frame, the LED element 7041 is mounted on the upper face of the
front end of the lead part 7004A. Next, one electrode on the upper
face of the LED element 7041 and the upper face of the lead part
7004A are connected to each other through a wire 7042, and,
further, the other electrode on the upper face of the LED element
7041 and the upper face of the lead part 7004B are connected to
each other through a wire 7042. Next, as explained above in
connection with the twentieth embodiment, the molding of the glass
material is carried out using a mold to form a sealing member 7005
having a predetermined shape. Finally, unnecessary parts in the
lead frame 7004 are removed to isolate individual luminescent
devices 7040 from the lead frame 7004.
In FIG. 98, for example, when the lead part 7004A is on the anode
side, a positive side of a direct current source (not shown) is
connected to the lead part 7004A, and a negative side is connected
to the lead part 7004B. Upon this energization, the LED element
7041 emits light. This light is emitted from the upper face of the
LED element 7041 and practically passes through the sealing member
7005 and goes to the outside of the sealing member 7005, and a part
of the light is internally reflected and goes to the outside of the
sealing member 7005.
In the twenty-first embodiment, in addition to the advantageous
effects of the twentieth embodiment, even in the case of the face
up-type luminescent device 7040, the occurrence of separation or
cracking can be prevented by taking into consideration the values
of coefficient of thermal expansion of the lead parts 7004A, 7004B
and the sealing member 7005 and using the low melting glass
material.
In the above embodiments, a reflecting surface may be formed on the
surface of the lead parts 7004A, 7004B for enhancing light outgoing
efficiency.
Further, a wavelength conversion part using a phosphor or the like
excited by a predetermined wavelength light may be provided within
the sealing member 7005 on the upper part of the LED elements 7001,
7042.
In the above embodiments, one LED element was provided within one
sealing member. Alternatively, however, two or more LED elements
may be provided to constitute a multi-emission-type luminescent
device. Regarding the type of the luminescent device in this case,
the construction shown in FIG. 94 which is of a flip chip bonding
type is suitable. In this case, a plurality of LED elements to be
mounted may be different from each other in emission color, or
alternatively the plurality of LED elements may be identical to
each other in emission color.
Further, regarding the drive mode of the LED elements, all of the
plurality of LED elements may be connected in parallel, or
alternatively a plurality of LED element groups may be connected in
parallel. Further, a plurality of LED elements may be connected in
series, or alternatively all the LED elements may be connected in
series.
Further, in the above embodiments, the sealing member 7005 is in a
semispherical form having a lens part on its top part. However, it
should be noted that the sealing member 7005 is not limited to the
form shown in the drawings, and any form such as a form not having
any lens part, a polygonal form, or a cylindrical form may be
adopted.
Furthermore, the glass sheet has been used in molding the sealing
member 7005. The method for sealing member formation is not limited
to the method using a glass sheet, and other sealing methods may
also be used.
FIG. 99 shows a flip chip-type luminescent device in the
twenty-second embodiment of the invention, wherein (a) is a
cross-sectional view and (b) a side view as viewed from the right
side face of (a). Parts having the same construction as those in
the twentieth embodiment are identified with the same reference
numerals. The construction of this luminescent device 7010 is that,
as shown in FIG. 99 (a), the submount element 7003 is mounted on a
heat dissipating part 7050 made of Cu followed by integral sealing
with a sealing member 7005 made of low melting glass. A lens 7005A
is provided in the sealing member 7005.
The submount element 7003 is received in a groove part 7051
provided in the heat dissipating part 7050, and a wiring pattern
7053 provided on its surface and the LED element 7001 in its
electrode are electrically connected to each other through the bump
7002 to constitute a part of the power supply part. After
connection to the LED element 7001, the wiring pattern 7053 is
soldered to the lead parts 7004A, 7004B made of Cu, a soft metal.
As shown in FIG. 99 (b), the lead part 7004B is placed in the
groove part 7051 through a glass material 7052 which is rectangular
in section and is in a rod form, and, in this state of insulation
from the heat dissipating part 7050, the sealing member 5 is heat
pressed. In this case, the lead part 7004A is also treated in the
same manner as in the lead part 7004B. The lead parts 7004A, 7004B
are integrated in such a state that the lead parts 7004A, 7004B are
insulated from the heat dissipating part 7050 by the glass material
7052 and sealing member 7005 which have been melted based on heat
pressing.
In the twenty-second embodiment, the heat dissipating part 7050 on
which the submount element 7003 has been mounted is integrally
sealed by the sealing member 7005 made of a glass material.
Therefore, in addition to advantageous effects in the first
embodiment, the dissipation of heat conveyed from the submount
element 7003 can be advantageously enhanced, and, thus, a
luminescent device 7001 can be provided in which excellent heat
dissipation can be realized in glass sealing, as well as, for
example, in the case where the quantity of heat generated from the
LED element 7001 by the flow of large current is increased, and
package cracks derived from a thermal expansion coefficient
difference are less likely to occur.
In the twenty-second embodiment, the construction using the heat
dissipating part 7050 made of Cu has been explained. However, other
materials, which have good thermal conductivity and are small in a
difference in coefficient of thermal expansion from the sealing
member 7005, for example, Cu alloys and aluminum may also be used.
When the heat dissipating part 7050 is made of aluminum, the
difference in coefficient of thermal expansion between the heat
dissipating part 7050, and the LED element 7001 and the submount
7003 is about 500%.
FIG. 100 shows a face up-type luminescent device in the
twenty-third embodiment of the invention, wherein (a) is a
cross-sectional view and (b) a side view as viewed from the right
side face of (a). Parts identical to those in the twenty-first
embodiment are identified with the same reference numerals. In this
luminescent device 70040, as shown in FIG. 100 (a), the LED element
7040 is bonded to the center of the heat dissipating part 50 made
of Cu. Lead parts 7004A, 7004B and the LED element 7040 in its
electrode for supplying electric power to the LED element 7040 are
electrically bonded to each other through a wire 7042. The LED
element 7040, the wire 7042, and the lead parts 7004A, 7004B are
covered by a silicone coating part 7060 made of a silicone resin so
as to withstand heat at the time of low melting glass sealing. The
sealing member 7005 covers the silicone coating part 7060 and, in
addition, is integrated with the heat dissipating part 7050. A lens
7005A is formed in the sealing member 7005.
In the twenty-third embodiment, even in the case of a face up-type
luminescent device 7040, glass sealing while preventing the
deformation of the electrode in the LED element 7041 and the wire
7042 caused by the pressure of the glass sealing becomes possible
by covering the periphery of the LED element 7041 with the heat
resistant and elastic silicone coating part 7060. Therefore, a
luminescent device 7001 can be realized which, in addition to
advantageous effects attained by the twenty-first embodiment, is
excellent in LED element 7041 mounting properties, and, in
addition, is good in heat dissipating properties not only during
glass sealing, but also, for example, in the case where the
quantity of heat generated from the LED element 7041 is increased
due to the use of large current and is less likely to cause package
cracking derived from a thermal expansion coefficient difference.
Further, the silicone coating part 7060 may contain a phosphor.
In the twenty-third embodiment, a construction has been explained
in which electric power is supplied to the LED element 7041 mounted
on the heat dissipating part 7050 from a pair of lead parts 7004A,
7004B. For example, a construction may also be adopted in which the
heat dissipating part 7050 is integrated with one lead part, and
the other lead part is insulated from the heat dissipating part
7050 through a glass material 7052.
In addition to the use of the silicone resin as the coating
material, other heat resistant materials such as ceramic coating
materials may be used. The construction in which the coating
material is applied is not limited to the face up-type LED element
and can be applied to flip chip-type LED elements.
In light emitting elements such as LEDs, when the refractive index
of the light emitting element is 2 or more, sealing of the element
with a sealing material with a refractive index of about 1.5 or
more can enhance the efficiency of takeout of light from the
element by about twice or more. In this case, the sealing material
should be transparent to light. In photodetectors, this effect
cannot be attained, and the effect attained by intimate contact
sealing of the element directly with the light transparent material
is only the effect of reducing reflection at interface between
dissimilar media. Light transparency is not required when the
element is not an optical element.
In the above embodiments, the sealing material is glass. The
sealing material, however, may be one obtained by crystallization
after glass processing, and may be any inorganic material so far as
it has high chemical stability.
INDUSTRIAL APPLICABILITY
As described above, according to the invention, even when a hard
glass material of 10.sup.8 to 10.sup.9 poises is used, sealing can
be carried out without damage to solid elements. Therefore, low
melting glass can be used, good glass sealing can be realized while
reducing thermal load applied to the solid elements. The
realization of a solid element device sealed with glass which, as
compared with resin materials, requires high temperature processing
and is a hard material that enables the solid element device to be
used in high-temperature environments and environments where
weathering resistance is required. Further, the adoption of light
transparent glass can realize such a high level of reliability that
the light transmittance of the optical device is stable and
undergoes no change with the elapse of time. Further, for the solid
light emitting element, when high refractive index glass is
selected, the efficiency of takeout of light from the light
emitting element can be improved and, consequently, highly
efficient luminescent devices can be realized.
* * * * *